Even more PackageManager caller triage.

Finish moving all UID/GID callers to single AIDL method that requires
callers to provide flags.

Triage AppWidgets and PrintServices, which currently can only live on
internal storage; we should revisit that later.

Fix two bugs where we'd drop pending install sessions and persisted
Uri grants for apps installed on external storage.

Bug: 26471205
Change-Id: I66fdfc737fda0042050d81ff8839de55c2b4effd