Persist framebuffer backing CLUT data to GS memory

[kernle32dll]

Dragonball Z Tenkaichi 2 renders its CLUT information into a framebuffer, and then tries to use it from there. This works for Vulkan, but for OpenGL the framebuffer content is never propagated back into the GS RAM, and thus unavailable when the CLUT information is required.

This PR uses a light-weight approach of reading framebuffer contents when required for CLUT calculation, and persists it (if not already done so). This works pretty well, and only decreases performance marginally.

Special note on the "downSample" part. For whatever reason, on resolution upscaling > 1 I got artifacts in the CLUT rendering. I don't know why, but down-sampling it in GPU memory again helped clear the issues.

[kernle32dll]

Master:

PR:

[Bogdans29]

Is Vulkan supported on android?

[ghost]

Any updates about this?