[sksl][compute][spirv] Support atomicUint

* Support the atomicUint type and atomicAdd/atomicLoad/atomicStore
  intrinsics in SPIR-V codegen.

* Support variable declarations in the workgroup address space.

Bug: b/262428625
Change-Id: I3777231a8bd41f58d21d21578a4bc51e8a060194
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/729098
Commit-Queue: Arman Uguray <armansito@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
5 files changed