Adds caller check to getAllPackages()

This change enforces that only system, root or shell may call
getAllPackages(), a hidden API that shares all package names regardless
of user, instant app or package visibility rules.

Bug: 174661955
Merged-In: I77460ae19a4d41151577646441f11e2eddbb741a
(cherry picked from commit cca5bf92)

Change-Id: I630cfd7c3be9bf6f2a6b8e132f6b8dda6b7fa274
(cherry picked from commit 264dea63)