Adds sampler serialization capability
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 <7c79ef580b4d963b83ede739cb9e40f930bcb4c9@google.com>
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Reviewed-by: Cody Northrop <94770d7fe1cce6ea0791fa9927c1107de4d2e37b@google.com>

ppy/angle,ppy/angle,ppy/angle,ppy/angle