Add Skip and TrySkip APIs to Utf8JsonReader with tests. (dotnet/corefx#37793)

Add Skip and TrySkip APIs to Utf8JsonReader with tests. (dotnet/corefx#37793)

* Add Skip and TrySkip APIs to Utf8JsonReader with tests.

* Auto-generate the ref assembly.

* Remove new lines and update bytes consumed to avoid adjusting OS specific offsets.

* Add IsFinalBlock public property.

* Break up the skip/try skip method into helpers.

* Add more direct tests and update impl to avoid unnecessary struct copy.

Commit migrated from https://github.com/dotnet/corefx/commit/2f2aca43ef9d24c794255c3ef5d0238dc479652b