Deprecate types in get, exists, and multi get.

[jtibshirani]

For each API, the following updates were made:

• 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).

[jpountz]

Can you add a description to the pull request here as well?

[elasticmachine]

Pinging @elastic/es-search

[jtibshirani]

I force-pushed because this PR was getting a bit messy, but it contains the same changes from when it was first reviewed, plus several fixes in integration tests to replace custom types with _doc.