Sync platform from Jetpack.

Included changes:
* caf5d9: Add a uri prefix to visibility store documents.
* 5b26a8: Minor comment fix in AppSearchSession
* 31b691: Add package visibility APIs for schema types.
* d36a2c: Require a package name in AppSearchImpl.

Bug: 169883602
Bug: 162450968
Test: Presubmit
Change-Id: I155145e4b14a271f3012cb7b5efbbe1b7ba27a18