The following updates were made:
- Add a new untyped endpoint `{index}/_explain/{id}`.
- Add deprecation warnings to Rest*Action, plus tests in Rest*ActionTests.
- For each REST yml test, make sure there is one version without types, and another legacy version that retains types (called *_with_types.yml).
- Deprecate relevant methods on the Java HLRC requests/ responses.
- Update documentation (for both the REST API and Java HLRC).
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