Previously, most StatsService calls only allow the caller to specify the
uid if it is Userdebug/EngBuild. This applied even if the caller was
just specifying its own UID; this cl allows such a case. It also allows
ROOT to impersonate SHELL.
Test: Manual testing on userdebug and userbuild devices.
Test: make statsd_test && adb sync data && adb shell data/nativetest64/statsd_test/statsd_test
Change-Id: I2685d13a8dc24d40b5dab8be9842f53be6888ba3
Statsd clients may want to set an empty config temporarily, so it's
more convenient to allow them to set an empty config instead of
having to use the removeConfig and then having to remember to call
StatsManager#setDataFetchOperation.
Test: Added unit-tests and check they pass on marlin-eng.
Bug: 74997752
Change-Id: I2e762e5ec01e5a2c9a3469fb330b53fefbd734d6
