Protect the default media PiP PendingIntent

- Add permission when register broadcast receiver
- Set receiver package explicitly when constructing PendingIntent
- Do not crash if there is no active media session when receive broadcast

Bug: 171967947
Test: adb unroot; adb shell am broadcast -a \
                      com.android.wm.shell.pip.PLAY
Change-Id: If9c46aab9d91de633a2628513430a59a6692e59a