ui/sdl2: reenable the SDL2 Windows keyboard hook procedure

ui/sdl2: reenable the SDL2 Windows keyboard hook procedure

Windows only:

The libSDL2 Windows message loop needs the libSDL2 Windows low
level keyboard hook procedure to grab the left and right Windows
keys correctly. Reenable the SDL2 Windows keyboard hook procedure.

Since SDL2 2.30.4 the SDL2 keyboard hook procedure also filters
out the special left Control key event for every Alt Gr key event
on keyboards with an international layout. This means the QEMU low
level keyboard hook procedure is no longer needed. Remove the QEMU
Windows keyboard hook procedure.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2139
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2323
Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Link: https://lore.kernel.org/r/20241231115950.6732-1-vr_qemu@t-online.de
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 4dafba778aa3e5f5fd3b2c6333afd7650dcf54e2)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(Mjt: context fix in ui/sdl2.c and adaptation in ui/meson.build)