Replace PackageManagerInternal with PackageManager.

PackageManagerInternal in LocaleManagerService allowed any app to query
for another app's existence by looking at the exception message thrown
by the LocaleManager's get/set APIs. External PM, on the other hand,
does package visibility filtering which restricts regular apps from
querying information about other apps.

Bug: 225881167
Bug: 226900861

Test: atest CtsLocaleManagerTestCases
Test: atest CtsLocaleManagerHostTestCases
Test: atest CtsBackupTestCases:AppLocalesBackupTest
Test: atest LocaleManagerServiceTest
Test: atest LocaleManagerBackupRestoreTest
Test: atest SystemAppUpdateTrackerTest
Test: Manually tested by flashing and verifying that the test app
(PocProject) attached in the bug is not able to query app existence, and
also verifying that Settings and PlayStore are able to get/set any app's
locales. Also tested multi-user and work profiles.

Change-Id: If00016e7afd7f6552b6c66984cc0194d1bc449b1