GL: Cache the results of glGetString To reduce the amount of queries to the driver, we can cache the results of glGetString. On Mac, we need to invalidate this cache on GPU switch. Bug: chromium:1173672 Change-Id: I039172068aec35034a87881a8804f52c080ce4ce Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2676882 Commit-Queue: Jonah Ryan-Davis <jonahr@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>