Features around findPath API.

* Add folders into search result
* Allow callers passing data to launch pickers at specfic location
* Rewire loadDocument() to LoadDocStackTask
* Remove VIEW intent for FilesActivity and related OpenUriForViewTask
* Add a ProviderAccess to enable testing in LoadDocStackTask
* Fix a wrong assertion in files/ActionHandlerTest

Change-Id: Iacc2b99dc68cbb4a40a4c445c69473973123c5bf