Vulkan: Fix incorrect DescriptorSet's bufferInfo in XFB emulation path The mAlignmentOffsets are pre-calculated at TransformFeedbackVK::begin() time but never gets updated when buffer changes after XFB begin call, which causes us sending down incorrect bufferInfo to the descriptor set. This CL removes mAlignmentOffsets and always calculate the aligned offset when mBufferOffsets is needed. This CL also modify the existing test to demonstrate the bug. Test: SimpleStateChangeTestES3.RespecifyBufferAfterBeginTransformFeedbackInDeletedPaddingBuffer Bug: angleproject:6998 Change-Id: I11a9f114385d2e49ba9bdc2d820727c85c8244dd Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3448682 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Charlie Lao <cclao@google.com>