Add operator<<(std::ostream&, ExecutionPlan::Kind)

Improves gtest failure messages that involve ExecutionPlan::Kind.

Test: Observed more-detailed failure messages from NeuralNetworksTest_static

Change-Id: I611238800c001aa758a7933650a9d9a531de078b
Merged-In: I611238800c001aa758a7933650a9d9a531de078b
(cherry picked from commit d77f8f3f87911d519ac79ec744efe17a7762ee0a)
1 file changed