Mocks depot_tool input_api and output_api for ANGLE
presubmit checks' unittests.
Adds unittests of ANGLE commit message format check

Bug: angleproject:4961
Change-Id: I2a8bc2c3703d9a07b26f7609490dbd80369c73b9
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2356287Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>