APIv4 - Add Contact::mergeDuplicates action

[colemanw]

Overview

Adds a mergeDuplicates APIv4 action, for parity with APIv3.

[civibot]

(Standard links)

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• If you are reviewing this pull-request, you may wish to consult the test sites and the Review Standards (long template, short template).

[tschuettler]

(CiviCRM Review Template DEL-1.2)

• General standards
  • Explain (r-explain)
    • PASS : The goal/problem/solution have been adequately explained with a link (JIRA, Github, Gitlab, StackExchange).
  • User impact (r-user)
    • PASS: The change would be intuitive or unnoticeable for a majority of users who work with this feature.
  • Documentation (r-doc)
    • PASS: The changes do not require documentation.
    • COMMENTS: I believe new actions are not added to the docs in general.
  • Run it (r-run)
    • PASS: Checked out PR locally and performed a merge with APIv3 and APIv4 via API explorer and CLI
    • COMMENTS: The test site was not online anymore. I thought those lasted a few days?
• Developer standards
  • Technical impact (r-tech)
    • PASS: The change preserves compatibility with existing callers/code/downstream.
  • Code quality (r-code)
    • PASS: The functionality, purpose, and style of the code seems clear+sensible.
  • Maintainability (r-maint)
    • PASS: The change sufficiently improves test coverage, or the change is trivial enough that it does not require tests.
  • Test results (r-test)
    • PASS: The test results are all-clear.
    • COMMENTS: I guess the test could have its own test class, but at least it is closely related to dupliates anyway.

[colemanw]

Thanks for the review @tschuettler