gl: Compute bringup and other improvements

[kd-11]

• Adds optional compute shaders to openGL for hardware that supports it.
• Reimplements imaging operations to make use of the compute framework. It may not seem obvious, but most drivers lack basic functionality when performing pack/unpack operations, making it so that copying memory from one image to another with a different pixel layout causes a flush-to-cpu to occur, where the driver does the transform using the cpu and then does another reupload. This destroys performance.

Makes OpenGL usable again on more mainstream hardware whereas before single digit framerates were the norm. See #6341

[RainbowCookie32]

GTA V's performance in OpenGL is now basically the same as Vulkan for me. The image seems to have noise with this PR though, but lighting seems to be better-ish

Comparison

-OpenGL Master

-OpenGL PR

-Vulkan Master

RPCS3.log.gz

[MarioSonic2987]

I can confirm the noise glitch, but it allows shadows to render correctly (no more dark shadows):

Saints Row: The Third is also affected by this PR. Now, lighting is now "correct":

Saints Row IV is also affected:

[jjsat]

With this PR the graphical isse from #5569 is fixed for me. It is still much slower on OpenGL (drops to 10s in busy scenes) than on Vulkan (usually solid 30).