Vulkan: Set varying location & xfb decorations in SPIR-V The shader translator outputs arbitrary location indices. Once compiled by glslang, the SPIR-V transformer modifies these decorations. If the transform feedback extension is used, it will also add the relevant decorations to the varyings that are captured. Bug: angleproject:3394 Change-Id: I5ecafd0536408612a5d4b920dbabbfabe650657c Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2008468 Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>