Adding API for retrieving the list of pre-installed system packages.

Launcher apps can use this API to identify system installed apps for
a given profile type.

The API is only accessible to system launcher ATM as it
can enlist activities in private space.
At a later point (b/303803157) this would be fine tuned.

Bug: 308054233
Test: atest LauncherAppsTest
Change-Id: Ifeb19580f13ced5e514244974d022749ed90031d