This change adds support for a new flag namely `--renderdoc` to end2end
and deqp tests.  With this flag, each test automatically starts and ends
a frame capture in renderdoc, working around an issue where renderdoc
refuses to capture a test frame that doesn't start or end with a swap.

With end2end tests, the capture starts before test set up, and ends
after test tear down.  With deqp tests, it starts before init, ends and
restarts after each test iteration and ends after deinit.

Bug: angleproject:6072
Change-Id: Ib41b816aff121bf922d9147044cc363c33a62181
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2971835
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>