Move packed enum code to common/ This makes it accessible in the utilities files. Bug: angleproject:2574 Bug: angleproject:2169 Change-Id: I0fdd34b4233e72b7534cb2b09f451539c1a394cd Reviewed-on: https://chromium-review.googlesource.com/1067110 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Yuly Novikov <ynovikov@chromium.org>