Validate package name passed to setApplicationRestrictions.

This adds validation that the package name passed to
setApplicationRestrictions is in the correct format. This will avoid
an issue where a path could be entered resulting in a file being
written to an unexpected place.

Bug: 239701237
Test: atest UserManagerServiceTest
Change-Id: I1ab2b7228470f10ec26fe3a608ae540cfc9e9a96
(cherry picked from commit 31a58249)
Merged-In: I1ab2b7228470f10ec26fe3a608ae540cfc9e9a96