[Windows] Use clear color for non exclusive fullscreen border, fix maximize for borderless window switching to exclusive fs.

[bruvzg]

• Changes multi-window full-screen border to use project "clear color".
• Fixes maximize for borderless window, which was switching to exclusive full-screen (required for [Client side decorations] Implement window drag handles. #80891).

[akien-mga]

Thanks!

[Calinou]

Regarding the border color, I wonder if it should always be black so that it's the least visible possible, especially on OLED displays. I notice the gray border quite a bit when running the 3D Platformer demo for instance, despite using a 42" 4K OLED display.

Of course, you can change the clear color to black in the Project Settings, but this may be undesired for some 2D projects during development.

Edit: Pull request opened: #88734