Refactor to avoid impacting JSON with RPCv2 logic

Motivation and Context

This change refactors the previously introduced (see #5543) logic to handle RPCv2 unmarshalling to move it into the RPCv2 package and keeping the JSON unmarshalling logic as it was.

In order to accomplish this we changed the way the unmarshaller gets its registry to allow it to be pass down using the protocol factory builder.

This will reduce the potential impact that this new protocol might have on the already existing ones.

Modifications

Testing

Screenshots (if appropriate)

Types of changes

[ ] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)

Checklist

[ ] I have read the CONTRIBUTING document
[ ] Local run of mvn install succeeds
[ ] My code follows the code style of this project
[ ] My change requires a change to the Javadoc documentation
[ ] I have updated the Javadoc documentation accordingly
[ ] I have added tests to cover my changes
[ ] All new and existing tests passed
[ ] I have added a changelog entry. Adding a new entry must be accomplished by running the scripts/new-change script and following the instructions. Commit the new file created by the script in .changes/next-release with your changes.
[ ] My change is to implement 1.11 parity feature and I have updated LaunchChangelog

License

[ ] I confirm that this pull request can be released under the Apache 2 license

aws / aws-sdk-java-v2

Refactor to avoid impacting JSON with RPCv2 logic #5544