[DO NOT MERGE] Use loadDrawableAsUser in MediaDataManager

This fixes a SystemUI loopcrash when casting as a guest user.

Bug: 173026465
Test: Manual - install media app that can cast on guest user only,
      then cast from guest user.  SystemUI should not crash.
Test: atest com.android.systemui.media
Change-Id: I70f5de89a813c54a616eb701a02aa43272754580