Also adds compiler tests for dynamic indexing of SSBOs and images.

Bug: angleproject:3569
Change-Id: I84b90813840ffad5a9a3cd8e7f12bd637a57b327
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1961095Reviewed-by: Jiajia Qin <jiajia.qin@intel.com>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>