Integer scaling

[Miss-Inputs]

This is an enhancement request and therefore subjective, but I think it'd be neat to have an option for integer scaling; such that if the guest resolution is (for example) 1600x900 and your host resolution is 1920x1080 you get black borders surrounding the screen instead of trying to have half-pixel scaling, which looks a bit ugly.

This can be achieved without an option by adding
SDL_RenderSetIntegerScale(sdl_renderer, SDL_TRUE);
above line 836 in video_sdl2.cpp, but it probably should be an option, because maybe some people are fine with non-integer scaling and whatnot and I'm not cool enough to figure out how to make it an option just yet.