add Method copyOf for MutablePair

[jack5505]

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[garydgregory]

Hello @jack5505

Good suggestion but there are a lot of changes needed.

To speed up the process, I've made these changes in git master.

You are credited in changes.xml.

You can close this PR once you validate your use case with a local build from git master or a snapshot build from https://repository.apache.org/content/repositories/snapshots/

Thank you.

[jack5505]

Build was successful