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

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