Added privacy toast for users first time using call composer.

When a user uses call composer for the first time, it isn't obvious that their
messages are being stored in the Android Messages app. So we display this toast
to them on the first time they make a enriched call to let them know for
privacy purposes.

screenshots:
http://screen/pcuu4GG037Z
http://screen/MLRJiY9V7cH
PiperOrigin-RevId: 159749893
Change-Id: I0cee7b49321f1d2302ba8ed8f6e1c19c44feb19a