Allow storage backends to publish multiple roots into the UI, which
are defined by a directory GUID, type, and label details. Update
external provider to surface a primary external storage root, and
switch to burning file path into the returned GUIDs so they remain
durable.
Added insert, update, and delete support to external provider. Adds
file extensions to display names when needed to match MIME type.
Add flags for searching and deletion, and extras for Cursor
pagination. Add directory creation dialog to UI. Opening a document
always gives write access.
Change-Id: I9bea1aa0dcde909a5ab86aefeece7451ab920cf1
Continuing to flesh out storage backends by adding an external
storage document backend. Still rough, but it can traverse files
and directories.
Early pass at OPEN/CREATE_DOC picker UI, which offers to traverse
any known storage backends. Supports opening subdirectories and
returning a picked file.
Change-Id: Idc3554036b3816a93d9b465ee8a620746859d2ae
