Vulkan: Support XFB in non-Vertex stages. This updates the code in several places to support Geometry and Tessellation Evaluation shaders to output transform feedback. Does not turn on any new tests but enables support for XFB when we turn on GS/TS. Bug: angleproject:3571 Bug: angleproject:3572 Change-Id: I6dcb768f2df4eeee81a4a500e999fcf16716f58f Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2581941 Reviewed-by: Tim Van Patten <timvp@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>