Add $clone as supported function

[HiroyasuNishiyama]

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Proposed changes

While editing JSONata, monaco editor do not show $clone as an candidate for completion.
This PR try to fix the issue.

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the forum/slack team.
• I have run grunt to verify the unit tests pass
• I have added suitable unit tests to cover the new/changed functionality

[coveralls]

Coverage remained the same at 68.341% when pulling 3eb2b2a on node-red-hitachi:support-clone-in-monaco into a5d7f7a on node-red:master.