SDL2 keyboard fixes on Windows

["Volker Rümelin" <vr_qemu@t-online.de>]

The Windows keys do not work properly with the SDL backend on Windows.
Patch 1/3 improves the situation. However, it's impossible to solve the
problem completely, as there is no way to grab the Windows keys. The
Windows keys are reserved for the operating system. In addition to
Ctrl-Alt-Del, there are other key combinations such as Win-Space or
Win-L where it's not possible to prevent the operating system from
executing the corresponding functions.

The other two patches prevent stuck modifier keys and unexpected text
input on Windows.

Volker Rümelin (3):
  ui/sdl2: reenable the SDL2 Windows keyboard hook procedure
  ui/sdl2: release all modifiers
  ui/sdl2: ignore GUI keys in SDL_TEXTINPUT handler

 include/ui/sdl2.h   |  2 ++
 ui/sdl2-input.c     |  5 ++++
 ui/sdl2.c           | 71 ++++++++++++++++++++++++++++-----------------
 ui/win32-kbd-hook.c |  3 ++
 4 files changed, 55 insertions(+), 26 deletions(-)

-- 
2.35.3