Adds sampler serialization capability Adds the ability to serialize sampler objects. Adds serialization of sampler objects to serializeContext method so that capture replay regression testing now compares the states of samplers too. Bug: angleproject:4817 Change-Id: Ic32d442eac9aa3afc5c9eea577522fe7054a755a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2315048 Commit-Queue: Manh Nguyen <nguyenmh@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Cody Northrop <cnorthrop@google.com>