Adds the ability to serialize GL context states.
Adds serialization of GL context states to serializeContext method so
that capture replay regression testing now compares the GL context
states.

Reformats frame_capture_utils to make most serialization methods
private, except for the ones called by other classes and template
methods.

Bug: angleproject:4817
Change-Id: I2d53c88be3d503268bd6e2e5058b5fabe0644f67
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2314829
Commit-Queue: Manh Nguyen <nguyenmh@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>