sokol_gfx.h: Readback API

[squk]

I'm curious if there's been discussion of a readback API. I have a Metal implementation working currently but unsure if it would be worth it to implement it for the other backends since I don't know if a readback API would be accepted/merged? If not I'll include the readback APIs in https://github.com/squk/sokol_utils instead :)

[floooh]

No immediate plans currently. There will eventually be a rewrite of the resource update functions (sg_update/append_*) to something that looks more like WebGPU (e.g. allowing GPU=>GPU, CPU=>GPU and ideally also GPU=>CPU copies, but the GPU=>CPU case will almost certainly have a completion callback (e.g. the result won't be available right after the function call).