Refactor: add InternalFormat::isInt() Bug: angleproject:3727 Change-Id: I33ee85563e3b070b4b86afc37230d3f5af54f446 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1713091 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>