Introduces enable_if handling for "FromGL". Avoids the use of any macro code to handle resource id casting. Bug: angleproject:3611 Change-Id: I1a6d10c3c9cc6ba0dc072bad1d62c33551f05d87 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1736127 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com>
