Add setting for customizable delimiter for file drag-and-drop (#19799)

## Summary of the Pull Request
This PR introduces a new profile setting, `dragDropDelimiter`, which
allows users to configure the string separator used when dragging and
dropping multiple files into the terminal. The default behavior remains
a single space (`" "`) for backward compatibility.

## References and Relevant Issues
* Closes #19565

## Detailed Description of the Pull Request / Additional comments
**Implementation Details:**
* **Settings:** Added `DragDropDelimiter` to `MTSMSettings.h` and
`Profile.idl`.
* **Control:** Wired the setting through `ControlProperties.h` so the
terminal logic can see it.
* **Logic:** Updated `TermControl::OnDrop` to use the new delimiter when
joining paths.
* **UI:** Added the text box in the Advanced Settings page and updated
the ViewModel.

## Validation Steps Performed
* **Manual Verification:**
    * Verified default behavior (space separator) works as before.
* Configured `dragDropDelimiter` to `", "`, `";"`, and custom strings in
`settings.json` and from settings UI.
    * Confirmed dropped files are joined correctly.
* **Build:** Validated that the solution builds cleanly.

## Notes for Reviewers
1. **Delimiter Length:** Currently, there is no limit on the maximum
length of the delimiter string. Let me know if this should be changed.
3.  **Localization:** I changed only `Resources/en-US` file.
4. **ViewModel:** In `ProfileViewModel.cpp`, I added the `else if` block
for the new setting, but left it empty because no other UI logic
currently depends on it.

## PR Checklist
- [x] Closes #19565
- [ ] Documentation updated
- [x] Schema updated (if necessary)

doc/cascadia/profiles.schema.json

@@ -3174,6 +3174,11 @@
             "mingw"
           ],
           "type": "string"
+        },
+        "dragDropDelimiter": {
+          "default": " ",
+          "description": "The delimiter used when dropping multiple files onto the terminal.",
+          "type": "string"
         }
       }
     },

src/cascadia/TerminalControl/IControlSettings.idl

@@ -76,6 +76,7 @@ namespace Microsoft.Terminal.Control
         Boolean RepositionCursorWithMouse { get; };
 
         PathTranslationStyle PathTranslationStyle { get; };
+        String DragDropDelimiter { get; };
 
         // NOTE! When adding something here, make sure to update ControlProperties.h too!
     };

src/cascadia/TerminalControl/TermControl.cpp

@@ -3060,7 +3060,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
     //   the full path of the file to our terminal connection. Like conhost, if
     //   the path contains a space, we'll wrap the path in quotes.
     // - Unlike conhost, if multiple files are dropped onto the terminal, we'll
-    //   write all the paths to the terminal, separated by spaces.
+    //   write all the paths to the terminal, separated by the configured delimiter.
     // Arguments:
     // - e: The DragEventArgs from the Drop event
     // Return Value:
@@ -3181,12 +3181,13 @@ namespace winrt::Microsoft::Terminal::Control::implementation
                 }
 
                 std::wstring allPathsString;
+                const auto delimiter{ _core.Settings().DragDropDelimiter() };
                 for (auto& fullPath : fullPaths)
                 {
-                    // Join the paths with spaces
+                    // Join the paths with the delimiter
                     if (!allPathsString.empty())
                     {
-                        allPathsString += L" ";
+                        allPathsString += delimiter;
                     }
 
                     const auto translationStyle{ _core.Settings().PathTranslationStyle() };

src/cascadia/TerminalSettingsAppAdapterLib/TerminalSettings.cpp

@@ -353,6 +353,7 @@ namespace winrt::Microsoft::Terminal::Settings
         _AllowVtChecksumReport = profile.AllowVtChecksumReport();
         _AllowVtClipboardWrite = profile.AllowVtClipboardWrite();
         _PathTranslationStyle = profile.PathTranslationStyle();
+        _DragDropDelimiter = profile.DragDropDelimiter();
     }
 
     // Method Description:

src/cascadia/TerminalSettingsEditor/ProfileViewModel.h

@@ -145,6 +145,7 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
         OBSERVABLE_PROJECTED_SETTING(_profile, AnswerbackMessage);
         OBSERVABLE_PROJECTED_SETTING(_profile, RainbowSuggestions);
         OBSERVABLE_PROJECTED_SETTING(_profile, PathTranslationStyle);
+        OBSERVABLE_PROJECTED_SETTING(_profile, DragDropDelimiter);
 
         WINRT_PROPERTY(bool, IsBaseLayer, false);
         WINRT_PROPERTY(bool, FocusDeleteButton, false);

src/cascadia/TerminalSettingsEditor/ProfileViewModel.idl

@@ -139,6 +139,7 @@ namespace Microsoft.Terminal.Settings.Editor
         OBSERVABLE_PROJECTED_PROFILE_SETTING(String, AnswerbackMessage);
         OBSERVABLE_PROJECTED_PROFILE_SETTING(Boolean, RainbowSuggestions);
         OBSERVABLE_PROJECTED_PROFILE_SETTING(Microsoft.Terminal.Control.PathTranslationStyle, PathTranslationStyle);
+        OBSERVABLE_PROJECTED_PROFILE_SETTING(String, DragDropDelimiter);
         OBSERVABLE_PROJECTED_PROFILE_SETTING(Boolean, AllowVtClipboardWrite);
     }
 }

src/cascadia/TerminalSettingsEditor/Profiles_Advanced.xaml

@@ -272,6 +272,16 @@
                           Style="{StaticResource ComboBoxSettingStyle}" />
             </local:SettingContainer>
 
+            <!--  Drag Drop Delimiter  -->
+            <local:SettingContainer x:Name="DragDropDelimiter"
+                                    x:Uid="Profile_DragDropDelimiter"
+                                    ClearSettingValue="{x:Bind Profile.ClearDragDropDelimiter}"
+                                    HasSettingValue="{x:Bind Profile.HasDragDropDelimiter, Mode=OneWay}"
+                                    SettingOverrideSource="{x:Bind Profile.DragDropDelimiterOverrideSource, Mode=OneWay}">
+                <TextBox Style="{StaticResource TextBoxSettingStyle}"
+                         Text="{x:Bind Profile.DragDropDelimiter, Mode=TwoWay}" />
+            </local:SettingContainer>
+
         </StackPanel>
     </Grid>
 </Page>

src/cascadia/TerminalSettingsEditor/Resources/en-US/Resources.resw

@@ -2748,4 +2748,12 @@
     <value>Type to filter icons</value>
     <comment>Placeholder text for a text box to filter and select an icon.</comment>
   </data>
-</root>
+  <data name="Profile_DragDropDelimiter.Header" xml:space="preserve">
+    <value>Drag and drop delimiter</value>
+    <comment>Header for a control to set the delimiter used when dragging multiple files into the terminal.</comment>
+  </data>
+  <data name="Profile_DragDropDelimiter.HelpText" xml:space="preserve">
+    <value>This text will be inserted between the paths of multiple files dropped into the terminal.</value>
+    <comment>A description for what the "drag drop delimiter" setting does.</comment>
+  </data>
+</root>

src/cascadia/TerminalSettingsModel/MTSMSettings.h

@@ -108,6 +108,7 @@ Author(s):
     X(bool, AllowVtChecksumReport, "compatibility.allowDECRQCRA", false)                                                                                       \
     X(bool, AllowVtClipboardWrite, "compatibility.allowOSC52", true)                                                                                           \
     X(bool, AllowKeypadMode, "compatibility.allowDECNKM", false)                                                                                               \
+    X(hstring, DragDropDelimiter, "dragDropDelimiter", L" ")                                                                                                   \
     X(Microsoft::Terminal::Control::PathTranslationStyle, PathTranslationStyle, "pathTranslationStyle", Microsoft::Terminal::Control::PathTranslationStyle::None)
 
 // Intentionally omitted Profile settings:

src/cascadia/TerminalSettingsModel/Profile.idl

@@ -94,5 +94,6 @@ namespace Microsoft.Terminal.Settings.Model
         INHERITABLE_PROFILE_SETTING(Boolean, AllowVtClipboardWrite);
 
         INHERITABLE_PROFILE_SETTING(Microsoft.Terminal.Control.PathTranslationStyle, PathTranslationStyle);
+        INHERITABLE_PROFILE_SETTING(String, DragDropDelimiter);
     }
 }

src/cascadia/inc/ControlProperties.h

@@ -87,4 +87,5 @@
     X(bool, ShowMarks, false)                                                                                                                            \
     X(winrt::Microsoft::Terminal::Control::CopyFormat, CopyFormatting, 0)                                                                                \
     X(bool, RightClickContextMenu, false)                                                                                                                \
-    X(winrt::Microsoft::Terminal::Control::PathTranslationStyle, PathTranslationStyle, winrt::Microsoft::Terminal::Control::PathTranslationStyle::None)
+    X(winrt::Microsoft::Terminal::Control::PathTranslationStyle, PathTranslationStyle, winrt::Microsoft::Terminal::Control::PathTranslationStyle::None)  \
+    X(winrt::hstring, DragDropDelimiter, L" ")