ShortcutManager: Support manifest shortcuts

- Now apps can publish shortcuts via AndroidManifest.xml
(Sample: I5b127150)

- Rename some APIs per API council feedback

- Publishers can now "disable" shortcuts.
(https://docs.google.com/presentation/d/1raUn1QBURDb1yrd6mSmVxII9ezNh3MWukODdtufJ29U/edit#slide=id.g13ef592464_7_39)

Bug 28785283
Bug 28536066

Change-Id: I4a126841e43e40139bb4baa6d0f98ad7b3a75ac1