Move JsonSerializer from libANGLE to common. This lets us use the serializer from outside of libANGLE. The plan is to use it to serialize a list of supported extensions from the tests. Bug: angleproject:6379 Change-Id: Ib7b64cca32e733e342b80f893d3752318089f0c2 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3163361 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>