This is a backport from the GTK-4.x update, so that we can aim to
support gtkglsink in gst-plugins-good even on Windows, beyond using
just Cairo in gstsink for rendering.
From the commit message in GTK-4.x, in commit 627ee674:
We might be dealing with GL contexts from different threads, which have more
gotchas when we are using libepoxy, so in case the function pointers for
these are invalidated by wglMakeCurrent() calls outside of GTK/GDK, such as
in GstGL, we want to use these functions that are directly linked to
opengl32.dll provided by the system/ICD, by linking to opengl32.lib.
This will ensure that we will indeed call the "correct" wgl* functions that
we need.
The old code used repeated calls to `ToUnicodeEx` to populate
the translation table, which is slow and buggy. The new code
directly loads the layout driver DLLs from Windows.
Associated issues: #2055#1033
Merge request: !1051
GdkWin32Keymap cleanup
Conform to C89, improve comments, whitespace
