Platform: request forward-compatible core context in Sdl2Application.
Platform: request forward-compatible core context in Sdl2Application.

Should avoid more potential issues when the driver has to return older
version because the newer has some features removed.

MiUishadow/magnum,MiUishadow/magnum,MiUishadow/magnum,MiUishadow/magnum,MiUishadow/magnum,MiUishadow/magnum