Clone preference values to our storage instead of direct assignment.
Adding a similar unit test from #7130.
Return a clone of the preference value instead of the actual one in our storage. Update the unit test to ensure this works as expected.
Clone pref objects for 'get' function only when the value is leaving the PreferencesSystem.
Merge pull request #7133 from adobe/rlim/clone-deep-prefs

Clone preference values to our storage instead of direct assignment.