Determines whether or not the given value is a measurement (or contains one).

Measurements are identified by the fact that any of them may have an _is_measurement_ method or cirq.measurement_keys returns a non-empty result for them.

val The value which to evaluate.
allow_decompose Defaults to True. When true, composite operations that don't directly specify their _is_measurement_ property will be decomposed in order to find any measurements keys within the decomposed operations.