Handle finished bugreports, share from private.

Show notification when a bugreport is finished, letting the user
launch a SEND_MULTIPLE intent to share them.  Add dialog that warns
user about contents before sharing.  Since bugreports are now stored
in private app data of the Shell app, use FileProvider to build Uris
that we can grant others access to.

Define BUGREPORT_FINISHED as being a protected broadcast.  Delete
older bugreports automatically to reclaim disk space.  Migrate any
Intent extras to ClipData when building PendingIntents.

Add --receiver-permission support to am shell command.

Bug: 7005318
Change-Id: If6c607dbcf137362d5887eac482ff7391563890f