Metal: refactor RenderUtils to split into multiple util classes. This is useful for later modifications where blit/clear could be further categorized based on texture format type (float/integer). Bug: angleproject:2634 Change-Id: I877abd21761af9e91657686a60e189a43a33e3f4 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2193195 Reviewed-by: Jonah Ryan-Davis <jonahr@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>