libANGLE: Minor cleanups. Removes a couple duplicated cached members in gl::State. Also a few other small refactorings. Bug: angleproject:5133 Change-Id: I0c6cd4c6544ef1690a4ce95d40dac70c688c7092 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3097808 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com> Reviewed-by: Cody Northrop <cnorthrop@google.com>