Complete validation of glGetAttribLocation() -Added more checks to glGetAttribLocation() similar to glBindAttribLocation(). -Added the corresponding unit tests. Using a reserved prefix in glGetAttribLocation() should return -1. Bug: angleproject:2419 Change-Id: I3f691f344c7003f855e53d35cd5f9578069acdae Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3252643 Commit-Queue: Amirali Abdolrashidi <abdolrashidi@google.com> Reviewed-by: Kenneth Russell <kbr@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>