Vulkan: SPIR-V Gen: Specialization constants With specialization constant qualifier and ids set in the node types, the SPIR-V generation for these variables are trivially handled. This is in preparation for enabling line raster emulation as well as fragment shaders in general. Bug: angleproject:4889 Change-Id: Ie4d4e47b222ac66d1e0eee29f55ac09990313580 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2939337 Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com>