Add: Option to (dis-)allow accelerated video drivers. (#8819)

The video drivers using the OpenGL backend are currently our only
accelerated drivers. The options defaults to off for macOS builds and
to on everywhere else.

Co-authored-by: Michael Lutz <michi@icosahedron.de>

src/video/sdl2_opengl_v.h

@@ -51,4 +51,7 @@ class FVideoDriver_SDL_OpenGL : public DriverFactoryBase {
 public:
 	FVideoDriver_SDL_OpenGL() : DriverFactoryBase(Driver::DT_VIDEO, 8, "sdl-opengl", "SDL OpenGL Video Driver") {}
 	/* virtual */ Driver *CreateInstance() const override { return new VideoDriver_SDL_OpenGL(); }
+
+protected:
+	bool UsesHardwareAcceleration() const override { return true; }
 };