On Windows, fix undecorated shadow reported client size is bigger than what's visible

[amrbashir]

• Tested on all platforms changed
• Added an entry to the changelog module if knowledge of this change could be valuable to users
• Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• Created or updated an example program if it would help users understand this functionality
• Updated feature matrix, if new features were added or implemented

Here is before:

And here is after:

[notgull]

Is there a way to reproduce this? Using the base example on the master branch, I don't see this on Windows 11.

(Looks good otherwise)

[amrbashir]

I have added an example in this PR that can be used to test this, just checkout this PR and revert the changes made to src/platform_impl/windows and you should see the bug, add back the changes from this PR and you should be able to see the fix.

I am also using Windows 11, the issue seems to happen only when undecorated shadows are active.

[amrbashir]

@notgull this should be ready now, thanks to implementation of the folks at GPUI, I tested different combination of decorations and undecorated shadows and all work as expected. I tested the implementation with winit and wry as well.

I have included an example in this PR that creates a window with a border on the reported surface size which can be used to compare with master branch.

[amrbashir]

This PR also has a good side effect that makes undecorated windows with shadows have native resize handles without explicitly handling WM_NCHITTEST like #2538 .

Undecorated windows with shadows are unaffected, would still need manual hittesting.