Vulkan: SPIR-V Gen: Apply Flat to int inputs in FS Not directly specified by the spec itself, but required according to this more generic statement: > Fragment shader inputs that are, or contain, integral types must be > qualified with the interpolation qualifier flat. This was previously fixed for gl_Layer in https://chromium-review.googlesource.com/c/angle/angle/+/3652746, but applies to gl_SampleID and gl_PrimitiveID as well. Bug: angleproject:7491 Change-Id: Ideae78ba57fe927ad0aa39460a5940dd5313ce9d Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3756612 Reviewed-by: Cody Northrop <cnorthrop@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>