Use the calling worksource uid for trusted apps.

- Set ThreadLocalWorkSource to the work source uid when app has the
UPDATE_DEVICE_STATS permission. We only enable that in system server for
now.
- By default, set ThreadLocalWorkSource to the calling uid since we
always trust this value.
- If an app sets a work source uid without having the right permission,
we just ignore it (we do not throw an exception)

A follow-up commit will update the code to use the worksource from the
beginning of the call. Currently we get the work source at the end
inside of BinderCallStats, however the value might have been changed
when executing onTransact.

Test: atest binderLibTest BinderWorkSourceTest BinderCallsStatsServiceTest
Change-Id: I351b8ac2b31feececc46c73f373f198b9b603c7e