Pass package name across binder.

Take the client's context package name and pass it across binder so we
can forward it to AppSearchImpl. We'll no longer be getting package name
from UID, but we'll still verify that the package name belongs to the
binder calling UID.

Bug: 177752194
Test: presubmit
Change-Id: I8aef10594a6130790e28fa34d87ab89717159d79