feat: support window transparency on Windows

[Nerixyz]

Extends #6137 to work on Windows. I only tested this on Windows 11.

[8thony]

On Windows 10, the window buttons get glitched, but there is no transparency on the window.
I used the normal Dark theme and the Transparent.json from the linked PR.
Tested on commit c513010
Note: You might have to restart for the buttons to get glitched.

Dark	Transparent

[Nerixyz]

On Windows 10

Thank you for testing on Windows 10!

the window buttons get glitched

One set of the window buttons is from Windows, because WS_SYSMENU, WS_MAXIMIZEBOX, and WS_MINIMIZEBOX are set. I don't remember if it's okay to unset these.

but there is no transparency on the window.

That's unfortunate. I can't really test on Windows 10 right now, so this will stay a draft for now.

Note: You might have to restart for the buttons to get glitched.

That's a problem on Linux as well (the implementation only changes the window transparency when creating the window).