Work around AM ContentObserver timing issue

For the CtsAngleDeveloperOptionHostTest tests we are seeing a flaky
failure in CTS and MTS testing. We tracked it down to a timing issue
with how/when the Activity Manager's cached settings values are updated.
Basically, we will set the settings to activate a particular code path
in GraphicsEnvironment and then run a test to check that behavior.
Sometimes, the test would fail. Logging showed that the test set the
values but the GraphicsEnvironment code path did not see the changes
because the Activity Manager's ContentObserver hadn't had time to
process the settings change. We can't read from the settings provider
directly because that has a huge performance impact and this is code
run during application startup.

Solution here is to add a command to ActivityManager to update it's
settings cache.
The test application then does:
Set setting.
Send AM refresh-settings-cache command.
At this time we know the cache is up-to-date and the test can run.

Test: atest android.angle.cts.CtsAngleDeveloperOptionHostTest
Bug: 148545737
Bug: 148546966
Change-Id: I7a12ce098315bb98eaafad122c770bfbfe67b988