Vulkan: SPIR-V Gen: Support geometry shaders Geometry shader built-ins are implemented. A bug in DeclarePerVertexBlocks is fixed w.r.t to gl_PerVertex arrays and a new AST validation option is added to catch that sort of error. Bug: angleproject:4889 Change-Id: I40b2929e450eac8ae840bbf1a1583e6c4c047c88 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3041623 Reviewed-by: Tim Van Patten <timvp@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>