GDK/Win32: Remove layered windows usage

Merged Chun-wei Fan requested to merge win32-remove-layered-windows into master


From the commit message, as a follow-up to 1, since we have been defaulting to use the OpenGL renderer on Windows for some time by now:

In GTK4, we are now defaulting to the OpenGL renderer with the Cairo renderer only used as a fallback, so there is no point keeping the code paths that use layered windows as layered windows do not work well with OpenGL nor Vulkan.

Please note that this is strictly for GTK master only, and we continue to use layered windows for our emulation of AeroSnap support for drawing the indicator.

With blessings, thank you!

Edited by Chun-wei Fan

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