Slight relaxing of ContextUserIdChecker.

Several managers keep an "int mUserId" field which is assigned from
Context.getUserId(), so Binder calls referencing that field are okay.

Also shift to borrowing the "flavor" logic for detecting userId
parameters consistently.

Bug: 115654727, 159626156
Test: atest error_prone_android_framework_test
Change-Id: I9841fdf16f34c08b113e689e74b94f1ede839e2c