fix(controls): Fix flickering issue when hovering over the top-right close button

[Koichi-Kobayashi]

Pull request type

• Update
• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes

What is the current behavior?

This pull request revisits and consolidates the changes from previous pull requests (#1647 and #1604).

It fixes an issue where the close button in the upper-right corner could flicker and become unresponsive when the mouse cursor was nearby, and restores the ability to resize the window from that corner.

Issue Number: #1647

What is the new behavior?

• Improved non-client-side hit testing for title bar buttons, reducing flickering during hover at pixel/DPI boundaries.
• Adjusted hit testing logic for TitleBar to prevent treating window button areas as resize/drag regions.
• Resolved merge conflict in src/Wpf.Ui/Controls/TitleBar/TitleBar.cs. ( my pull request fix(controls): Enable window resizing from title bar corners #1604 )

Other information

N/A