CL/Vulkan: Rework spec constant handling Specialization constants can be combined into a single hash map that's later iterated on when we create the compute pipeline. Bug: angleproject:364396920 Change-Id: I161356808ff0bd6a589f01854264210011bec512 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5834664 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Austin Annestrand <a.annestrand@samsung.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>