Activity Action: Allow the user to pick a directory subtree. When invoked, the system will display the various Android.Provider.DocumentsProvider instances installed on the device, letting the user navigate through them. Apps can fully manage documents within the returned directory.
To gain access to descendant (child, grandchild, etc) documents, use Android.Provider.DocumentsContract.BuildDocumentUriUsingTree(Android.Net.Uri, System.String) and Android.Provider.DocumentsContract.BuildChildDocumentsUriUsingTree(Android.Net.Uri, System.String) with the returned URI.
Output: The URI representing the selected directory tree.