Allow application to inspect query-ability of other package

This CL creates a new API PackageManager#mayPackageQuery for
applications that share details about other applications to
determine if those details should be withheld from callers
that do not otherwise have visibility of them.

Bug: 145916881
Test: atest AppEnumerationTests
Change-Id: I2dfba1169bce3d9fa88a75c92a22f53e1efe01b5