Vulkan: Reduce the onBufferRead/onBufferWrite API verbosity a bit This adds helper functions to handle common use case for onBufferRead and onBufferWrite to reduce the API verbosity a little bit. Also fix the transform feedback bug that we are passing in wrong access/stage flags when it is emulated by vertex shader. Bug: b/155122200 Change-Id: Id2549ca00cad184a90c6230dc3665aaff44dda08 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2174265 Commit-Queue: Charlie Lao <cclao@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>