When an isolated process calls Context.getSharedPreferences it fails

(as expected) because it calls into UserManager which is not allowed
for an isolated process.

This CL adds an extra error message for these calls so that the
application knows not to do this.

Bug: 304579365
Test: None
Flag: None
Change-Id: I3a7fa755e3c1315339cd25f33d3c6d7bff0da802