[Migrated] `OpConvertUToPtr` support

Issue automatically imported from old repo: https://github.com/EmbarkStudios/rust-gpu/issues/767
Old labels: t: enhancement,s: qptr may fix
Originally creatd by expenses on 2021-10-13T09:10:25Z

I started looking into how OpConvertUToPtr can be implemented - initially for RuntimeArrays. Something like this works well, but is not generic:

unsafe fn load_f32_runtime_array_from_handle(handle: u64) -> &'static mut RuntimeArray<f32> {
    asm!(
        "%f32 = OpTypeFloat 32",
        "%runtime_array = OpTypeRuntimeArray %f32",
        "%runtime_array_ptr = OpTypePointer Generic %runtime_array",
        "%result = OpConvertUToPtr %runtime_array_ptr {handle}",
        "OpReturnValue %result",
        handle = in(reg) handle,
        options(noreturn)
    )
}

I know that @msiglreith implemented loading resources from handles in https://github.com/EmbarkStudios/rust-gpu/compare/main...msiglreith:glace, but it looks like that requires a lot of codegen changes - ideally we should keep things at the asm! layer if possible.

Is there a way to make the above function generic over T, or will this require a few codegen changes?

Start with the asm! example in the issue and the linked glace comparison to understand how resource handles and OpConvertUToPtr are currently approached. Determine whether generic support can stay at the asm! layer or requires codegen changes; the work is done when that scope is established and the requested support is implemented.