Vulkan: Move SPIR-V generators to base transformer class Moves the generators from SpirvVertexAttributeAliasingTransformer to the base class, and makes SpirvTransformer use the same functions. Bug: angleproject:4889 Change-Id: I1f105e2ac764fc7b36c8c75d2cf5f30dec841f97 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2561938 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>