[sksl] Support all compute stage inputs

Added support for all compute stage builtin input variables using
the GLSL style sk_NumWorkgroups, sk_WorkgroupID, sk_LocalInvocationID
sk_GlobalInvocationID, sk_LocalInvocationIndex.

These variables very closely match the corresponding variable names in
OpenGL, Vulkan, and WebGPU. They also very specifically capture each
variable's meaning and domain compared to the existing

Bug: b/259564222
Change-Id: Ida8425c47d54072ac48051032fe9a4965f7ea98d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/609016
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Arman Uguray <armansito@google.com>
29 files changed