fix: CSD window frame tiles properly on Wayland

[mitchchn]

Description of Change

On Wayland compositors that use CSD (GNOME), tiled windows had a non-tiled appearance with rounded corners and shadows on all sides, and they showed resize handles on all edges.

Reasons for the issue:

1. A bug in the GNOME compositor on Ubuntu reports all edges as tiled even if only some are. (This also affected Chrome: https://issues.chromium.org/issues/454083284.)
2. The CSD frame was applying positive insets on all sides of the frame, when only the visible edges should have insets when tiled/maximized.

Some issues with tiling and resize handles were addressed previously in #46155. This PR fully restores the correct tiled appearance and behaviours without regressing those fixes.

Relates to #45916. This PR fixes tiling resize handles for CSD windows, but not (yet) for fully frameless windows (frame: false/WCO) because this technique requires a GTK client frame. This solution will however also apply to frameless windows when they get a client frame + shadows.

Before:

After:

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• tests are changed or added
• relevant API documentation, tutorials, and examples are updated and follow the documentation style guide
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Corrected the appearance of tiled windows on GNOME (when frame: true), and removed resize handles from tiled edges.

[codebytere]

@mitchchn i pulled the branch down and ran it - and I still see this:

I'm running Wayland on Ubuntu 24.04, using the default Fiddle. Is there anything I'm missing?

[mitchchn]

@codebytere this PR is for window tiling which isn't in your screenshot. When you tile left/right, you should now see:

1. No shadows on the free edge
2. Square corners on the tiled edges
3. Resize handles only on the free edge

(If you are talking about the window titlebar buttons being on the wrong side, that was fixed in a different PR, but you can't yet tell in Fiddle because its version of Electron still sets the old environment variable which propagates to child processes.)

[release-clerk]

Release Notes Persisted

Corrected the appearance of tiled windows on GNOME (when frame: true), and removed resize handles from tiled edges.

[trop]

I have automatically backported this PR to "39-x-y", please check out #48834

[trop]

I have automatically backported this PR to "40-x-y", please check out #48835

[trop]

I have automatically backported this PR to "38-x-y", please check out #48836