Gets a handle to the system’s key/value state. THe key/value state is only accessible if the
function is executed on a KeyedStream. On each access, the state exposes the value for the
key of the element currently processed by the function. Each function may have multiple
partitioned states, addressed with different names.
Because the scope of each value is the key of the currently processed element, and the
elements are distributed by the Flink runtime, the system can transparently scale out and
redistribute the state and KeyedStream.