Metal: add test for active blit/compute & render encoder mistracking. The bug was already fixed but we need to add the test to avoid the issue from resurfacing in future. Bug: angleproject:8685 Change-Id: Ia10c0954ef39b20b1d891389b7e7a1c81cdc758d Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5514529 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Quyen Le <lehoangquyen@chromium.org>