Introduce SelfExecutingMonitor for tests.

A number of tested components rely on monitors for pretext conditions.
In these cases, a mocked monitor will not execute the callback in order
for the logic to proceed. This change introduces and integrates
SelfExecutingMonitor to handle this case.

Bug: 261420432
Test: atest ComplicationTypesUpdaterTest
Test: atest DreamClockTimeComplicationTest
Test: atest DreamHomeControlsComplicationTest
Test: atest SmartSpaceComplicationTest
Change-Id: I2368bdcaa8a8a064484c160ddd95bf73882b733d