Add a shell command for distraction restrictions

Test: adb shell pm set-distracting-restriction
E.g.
adb shell pm set-distracting-restriction --flag hide-notifications \
com.android.chrome
Then, verify the distractionFlags shown in
adb shell dumpsys package com.android.chrome

Fixes: 169841816
Change-Id: Ic056cb33759a9e36f722c3b3622d9f714ab668c8