Fix font face keyboard selection crash (#20255)

## Summary

Fixes a crash in the Settings UI font face control when selecting a font
suggestion with the keyboard and pressing Enter.

The font face `AutoSuggestBox` path was explicitly unfocusing the box
after a chosen suggestion was submitted. During the keyboard suggestion
commit path, that `Focus(FocusState::Unfocused)` call can trigger a
WinUI/XAML crash before the settings model update completes.

This change avoids explicitly unfocusing the `AutoSuggestBox` in the
chosen-suggestion path and instead commits the selected font and moves
focus to the parent container.

Fixes #20245.

## Validation

Manually validated with a local `CascadiaPackage` Debug x64 build:

- Reproduced the crash before the fix.
- Opened Settings → Defaults → Appearance → Font face.
- Typed a partial font name.
- Used arrow keys to select a suggestion.
- Pressed Enter.
- Verified Terminal no longer crashes.
- Verified the selected font is applied and Save works.

src/cascadia/TerminalSettingsEditor/Appearances.cpp

@@ -12,6 +12,7 @@
 #include "Appearances.g.cpp"
 
 using namespace winrt::Windows::UI::Text;
+using namespace winrt::Windows::UI::Core;
 using namespace winrt::Windows::UI::Xaml;
 using namespace winrt::Windows::UI::Xaml::Controls;
 using namespace winrt::Windows::UI::Xaml::Data;
@@ -1221,8 +1222,6 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
             fontSpec = fontName;
         }
 
-        sender.Text(fontSpec);
-
         // Normally we'd just update the model property in LostFocus above, but because WinUI is the Ralph Wiggum
         // among the UI frameworks, it raises the LostFocus event _before_ the QuerySubmitted event.
         // So, when you press Save, the model will have the wrong font face string, because LostFocus was raised too early.
@@ -1233,11 +1232,20 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
         // You can't just do IsSuggestionListOpen(false) either, because you can show the list with that property but not hide it.
         // So, we update the model manually and assign focus to the parent container.
         //
-        // BUT you can't just focus the parent container, because of a weird interaction with AutoSuggestBox where it'll refuse to lose
-        // focus if you picked a suggestion that matches the current fontSpec. So, we unfocus it first and then focus the parent container.
-        _updateFontName(fontSpec);
-        sender.Focus(FocusState::Unfocused);
-        FontFaceContainer().Focus(FocusState::Programmatic);
+        // Queue the selected-suggestion commit so AutoSuggestBox can finish processing Enter before we change its text/model.
+        // Do not manually unfocus the AutoSuggestBox here. Its Focus(FocusState::Unfocused) path crashes during keyboard commits.
+        Dispatcher().RunAsync(CoreDispatcherPriority::Normal, [weakThis{ get_weak() }, weakSender{ winrt::make_weak(sender) }, fontSpec{ std::move(fontSpec) }]() {
+            if (const auto self{ weakThis.get() })
+            {
+                if (const auto box{ weakSender.get() })
+                {
+                    box.Text(fontSpec);
+                }
+
+                self->_updateFontName(fontSpec);
+                self->FontFaceContainer().Focus(FocusState::Programmatic);
+            }
+        });
     }
 
     void Appearances::FontFaceBox_TextChanged(const AutoSuggestBox& sender, const AutoSuggestBoxTextChangedEventArgs& args)