Test Runner: Handle GTest sharding args. These were messing up the test runner when used in combination with the test runner's specific args. Make it an error if the arguments are used together. Bug: angleproject:3162 Change-Id: I6fa1c0fb346a8c376ca455f7f4bf0492cfc0198a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2414931 Reviewed-by: Yuly Novikov <ynovikov@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>