Changes instances where we were querying 'color buffers' and 'depth
buffers' to 'color attachments' and 'depth attachments', etc.

Bug: angleproject:3611
Change-Id: I7af7d33e5204f21d288f5bcad997988d36eabfc5
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1690679
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>