The shader translator outputs arbitrary location indices for vertex
attributes.  Once compiled by glslang, the SPIR-V transformer modifies
these decorations.

Bug: angleproject:3394
Change-Id: I88453b44e3a8770f51e79228148233ff308f1885
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2011212
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>