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/+/2193195Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>