[ainulindale] fix defterm

Each page was registering as a handoff target, so basically we'd start the
  server then yeet the connection back to the first window and presto, you'd
  have a dead window and a connection on the wrong thread and everything was
  awful. Instead, only register as the handoff listener when we've actually said
  we want to be a handoff listener.

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -228,9 +228,6 @@ namespace winrt::TerminalApp::implementation
         // Hookup our event handlers to the ShortcutActionDispatch
         _RegisterActionCallbacks();
 
-        // Hook up inbound connection event handler
-        ConptyConnection::NewConnection({ this, &TerminalPage::_OnNewConnection });
-
         //Event Bindings (Early)
         _newTabButton.Click([weakThis{ get_weak() }](auto&&, auto&&) {
             if (auto page{ weakThis.get() })
@@ -519,6 +516,9 @@ namespace winrt::TerminalApp::implementation
         {
             _shouldStartInboundListener = false;
 
+            // Hook up inbound connection event handler
+            _newConnectionRevoker = ConptyConnection::NewConnection(winrt::auto_revoke, { this, &TerminalPage::_OnNewConnection });
+
             try
             {
                 winrt::Microsoft::Terminal::TerminalConnection::ConptyConnection::StartInboundListener();
@@ -3326,6 +3326,8 @@ namespace winrt::TerminalApp::implementation
 
     HRESULT TerminalPage::_OnNewConnection(const ConptyConnection& connection)
     {
+        _newConnectionRevoker.revoke();
+
         // We need to be on the UI thread in order for _OpenNewTab to run successfully.
         // HasThreadAccess will return true if we're currently on a UI thread and false otherwise.
         // When we're on a COM thread, we'll need to dispatch the calls to the UI thread

src/cascadia/TerminalApp/TerminalPage.h

@@ -226,6 +226,8 @@ namespace winrt::TerminalApp::implementation
 
         PaneResources _paneResources;
 
+        winrt::Microsoft::Terminal::TerminalConnection::ConptyConnection::NewConnection_revoker _newConnectionRevoker;
+
         winrt::Windows::Foundation::IAsyncOperation<winrt::Windows::UI::Xaml::Controls::ContentDialogResult>
         _ShowDialogHelper(const std::wstring_view& name);