gmock-actions_test depends on order of test execution

In gmock-actions_test, tests

• MockMethodTest.CanReturnMoveOnlyValue_Invoke and
• DefaultValueTest.GetWorksForMoveOnlyIfSet

both change DefaultValue<std::unique_ptr<int>>::producer_ without restoring the state after the test.

This causes the following failures:

1. DefaultValueTest.GetWorksForMoveOnlyIfSet fails when it is executed after MockMethodTest.CanReturnMoveOnlyValue_Invoke.
   With 50% chance, the following call fails:
   gmock-actions_test --gtest_filter="MockMethodTest.CanReturnMoveOnlyValue_Invoke:DefaultValueTest.GetWorksForMoveOnlyIfSet" --gtest_shuffle

2. DefaultValueTest.GetWorksForMoveOnlyIfSet fails when it is executed repeatedly:
   gmock-actions_test --gtest_filter="DefaultValueTest.GetWorksForMoveOnlyIfSet" --gtest_repeat=2

In practice, we observed the problem when executing googletest’s own unit tests on AIX (without shuffle, without repeat), because the test execution order was different than on other platforms.

Since the order of test execution is undefined, the tests should work in any order.

Locally, we fixed the problem by adding the line
DefaultValue<std::unique_ptr<int>>::Clear();
at the end of both tests.