Disable rounded window corners on Windows

[pkdawson]

I noticed when reading the latest Dolphin progress report that it's actually possible to disable the rounded corners in Windows 11.

I feel like this is a desirable change for games in general, as it actually shows everything you render instead of hiding the bottom corners, which is particularly annoying when taking screenshots.

I suppose the argument against would be that it's inconsistent with the Windows 11 default, so non-game applications might look slightly odd to a user.

[frkntlr]

Appears without rounded corners in Windows 10.

[Repiteo]

Note that Dolphin only applies the sharp corners for the game window; all other windows still retain the default, rounded style:

[pkdawson]

Yeah makes sense, since the editor should always have empty space in the bottom few pixels, the corners don't really matter.

[Hilderin]

That will change a default Windows behavior. I guess for games it's great but for applications created with Godot, they probably prefers rounded corners. I think a new flag to deactivate the rounded corner should be a preferred and move flexible way. With a new flag, the condition on specific Engine window in DisplayServerWindows could be replaced by this new flag.