Added doOnTearDown on MonotonicClockTestScope.

This is useful for ensuring resources are released, listeners are
unregistered, or subscriptions are cancelled, regardless of the test
outcome. The actions are executed in the order they were added.

Example Usage:

@Test
fun myTest() = runMonotonicClockTest {
    val myResource = acquireResource()
    doOnTearDown { myResource.release() }

    // ... test code using myResource ...
}

Test: atest RunMonotonicClockTestTest
Bug: 384402480
Flag: NONE test util
Change-Id: I964c4ea4da690ac1a378d5dd4bf1dc54616df189
2 files changed