RingtonePlayer: URI userId must match that of caller

Prevent one user from playing media from another user
by checking that the userId of the content matches
the userId of the caller.

Bug: 300654867
Test: see POC, needs to also be tested from 2ndary user
Flag: EXEMPT for security

Change-Id: I5914270c3421650eeb97f1b329a4aeb613f57b90