Allow software renderer to simulate vsync

[weirddan455]

Vsync was enabled in the software renderer but it only gave a hint to apply to a potential hardware accelerated framebuffer.

This adds a check to see if we are on a full software path (or otherwise didn't get vsync) and simulate it if the application requests vsync.

Let me know if that WindowTextureData declaration needs to go somewhere else. Wasn't really sure what header to put it in.

Some history I dug up if you're interested. Issue and commit for enabling vsync in software (last year):
#4612
fcfd19d

Issue and commit for the simulated vsync (just last month):
#5134
d744aaf

[weirddan455]

Btw I tested behavior by setting the SDL_HINT_FRAMEBUFFER_ACCELERATION hint. Before if that hint was set to 0, and SDL_RENDERER_SOFTWARE | SDL_RENDERER_PRESENTVSYNC was requested in SDL_CreateRenderer, it would get 500+ FPS. Now, it's mostly equal to my refresh rate.

If hint is set to 1, it uses real vsync from the hardware (same behavior).

[slouken]

@weirddan455, I'd like to get this into the SDL 3.0 release, can you update your PR?

[slouken]

We have simulated vsync in for SDL 3.0, thanks!