[Api] Introduce ProcessFunction and RuntimeContext related interfaces #1

Job	Run time
Pre-compile Checks / Basic QA	6m 15s
Default (Java 8) / Compile	25m 57s
Default (Java 8) / Test packaging/licensing	5m 23s
Default (Java 8) / E2E (group 1)	2h 1m 54s
Default (Java 8) / Test (module: core)	36m 3s
Default (Java 8) / E2E (group 2)	2h 23m 8s
Default (Java 8) / Test (module: python)	1h 30m 25s
Default (Java 8) / Test (module: table)	29m 55s
Default (Java 8) / Test (module: connect)	18m 48s
Default (Java 8) / Test (module: tests)	45m 1s
Default (Java 8) / Test (module: misc)	45m 10s
	9h 27m 59s

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