[SPARK-11681][Streaming] Correctly update state timestamp even when state is not updated #9648
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Bug: Timestamp is not updated if there is data but the corresponding state is not updated. This is wrong, and timeout is defined as "no data for a while", not "not state update for a while".
Fix: Update timestamp when timestamp when timeout is specified, otherwise no need.
Also refactored the code for better testability and added unit tests.