WebGPU support

[Seyedof]

@bkaradzic Is there a reason you recently dropped webgpu API support?
Is it a temporary decision or something permanent?
I remember once you said you're not going to maintain the webgpu backend until webgpu is released and settled in major web browsers, which actually happened in 2023, Chrome and Edge have it and more browsers coming.

There are certain features available in webgpu like indirect draw calls which are not possible in WebGL, perhaps now is the right time to do add proper WebGPU implementation to bgfx, kinda future proof thing.
What do you think?

[bkaradzic]

Justification for removal is:

• WebGPU not being ready in all browsers as of 11/2023.
• Code rot of code in bgfx due lack of maintainer (code not touched in 2+ years).
• Even if code is updated, there is no clear path from shaderc GLSL to WGSL.

Once W3C finalize specs and becomes available in Safari and Firefox by default, support will be reevaluated.