DirectX 12 Renderer (#5761)

* DirectX 12 Renderer (27 squashed commits)

* Add missing SDL_hidapi.h of merge of SDL.vcxproj.filters

* Fixed OpenWatcom build failure

* Dynapi fix

Co-authored-by: Ryan C. Gordon <icculus@icculus.org>

include/SDL_hints.h

@@ -1200,6 +1200,8 @@ extern "C" {
  *
  *  This variable is case insensitive and can be set to the following values:
  *    "direct3d"
+ *    "direct3d11"
+ *    "direct3d12"
  *    "opengl"
  *    "opengles2"
  *    "opengles"