fix(resizePane): Mark as handled only when resize succeeds (#20001)

This fix addresses issue #19983 where resizePane actions unconditionally
consume keystrokes even when no resize can occur.

The fix follows the same pattern used for moveFocus and swapPane fixes:
- Changed Tab::ResizePane to return bool indicating success
- Changed TerminalPage::_ResizePane to return bool from ResizePane  
- Updated _HandleResizePane to set args.Handled() based on whether
resize succeeded

This allows the keychord to propagate to the terminal when no resize can
occur, matching the behavior of moveFocus and swapPane (#6129).

Closes #19983

---------

Co-authored-by: nmurrell07 <nmurrell07@users.noreply.github.com>
Co-authored-by: Dustin L. Howett <dustin@howett.net>

Author: nmurrell07

src/cascadia/TerminalApp/AppActionHandlers.cpp

@@ -499,8 +499,8 @@ namespace winrt::TerminalApp::implementation
             }
             else
             {
-                _ResizePane(realArgs.ResizeDirection());
-                args.Handled(true);
+                const auto resizeSucceeded = _ResizePane(realArgs.ResizeDirection());
+                args.Handled(resizeSucceeded);
             }
         }
     }

src/cascadia/TerminalApp/Tab.cpp

@@ -844,14 +844,14 @@ namespace winrt::TerminalApp::implementation
     // Arguments:
     // - direction: The direction to move the separator in.
     // Return Value:
-    // - <none>
-    void Tab::ResizePane(const ResizeDirection& direction)
+    // - whether a pane was resized
+    bool Tab::ResizePane(const ResizeDirection& direction)
     {
         ASSERT_UI_THREAD();
 
         // NOTE: This _must_ be called on the root pane, so that it can propagate
         // throughout the entire tree.
-        _rootPane->ResizePane(direction);
+        return _rootPane->ResizePane(direction);
     }
 
     // Method Description:

src/cascadia/TerminalApp/Tab.h

@@ -53,7 +53,7 @@ namespace winrt::TerminalApp::implementation
                                                                                                         const float splitSize,
                                                                                                         winrt::Windows::Foundation::Size availableSpace) const;
 
-        void ResizePane(const winrt::Microsoft::Terminal::Settings::Model::ResizeDirection& direction);
+        bool ResizePane(const winrt::Microsoft::Terminal::Settings::Model::ResizeDirection& direction);
         bool NavigateFocus(const winrt::Microsoft::Terminal::Settings::Model::FocusDirection& direction);
         bool SwapPane(const winrt::Microsoft::Terminal::Settings::Model::FocusDirection& direction);
         bool FocusPane(const uint32_t id);

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -2900,14 +2900,15 @@ namespace winrt::TerminalApp::implementation
     // Arguments:
     // - direction: The direction to move the separator in.
     // Return Value:
-    // - <none>
-    void TerminalPage::_ResizePane(const ResizeDirection& direction)
+    // - whether a pane was resized
+    bool TerminalPage::_ResizePane(const ResizeDirection& direction)
     {
         if (const auto tabImpl{ _GetFocusedTabImpl() })
         {
             _UnZoomIfNeeded();
-            tabImpl->ResizePane(direction);
+            return tabImpl->ResizePane(direction);
         }
+        return false;
     }
 
     // Method Description:

src/cascadia/TerminalApp/TerminalPage.h

@@ -426,7 +426,7 @@ namespace winrt::TerminalApp::implementation
                         const Microsoft::Terminal::Settings::Model::SplitDirection splitType,
                         const float splitSize,
                         std::shared_ptr<Pane> newPane);
-        void _ResizePane(const Microsoft::Terminal::Settings::Model::ResizeDirection& direction);
+        bool _ResizePane(const Microsoft::Terminal::Settings::Model::ResizeDirection& direction);
         void _ToggleSplitOrientation();
 
         void _ScrollPage(ScrollDirection scrollDirection);