Render sprites to an off-screen area to reduce artifacts

[luksamuk]

This task is a technical debt for #7 and may depend on most VRAM mappings being used, so most VRAM-related features must be at least working until this change is made.

This task will prevent a bug that makes animation tiles way to apparent when Sonic's sprite is rotated. By rendering the sprite frame to an off-screen texture in VRAM, we can take this pre-rendered frame and rotate or flip it with no artifacts since it will work as a single quad.

Further, this will probably boost performance since we could use SPRT_8 for the off-screen rendering.

[luksamuk]

This is still a wanted enhancement, but I think we might not need this.