* convert functional_tests/lib into TS
* convert ES cluster factory into TS
* fix exports from kbn-test
* fix core test_helpers
* remove legacy ES client usage in ui_settings tests
* remove unnecessary ts-expect-errors comments
* initialize DEFAULT_SETTINGS_WITH_CORE_PLUGINS lazily to prevent failure when imported outside of FTR context
* throw an exception on invalid process.env.TEST_ES_PORT