Tests for the upcoming implementation of vertex attribute aliasing in
Vulkan.

Bug: angleproject:4249
Change-Id: Ic87e44b1815b376da4cda5e8887dd3a05c9cc35f
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2477051Reviewed-by: Charlie Lao <cclao@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>