Expose @SystemApi and @Public for unbundling DocumentsUI

1. Expose @Public for query arguments and flags.
2. Expose @SystemApi for related manageMode apis and some
   related storage flag in Root.
3. Add new isChildDocument method to support ContentResolver
   parameter and expose it @Public.
4. Expose @Public for getDocumentMetadata related methods.

Bug: 117634543
Test: make, make api-stubs-docs-update-current-api,
Change-Id: Ib172d46ba9727c35277fb285d3a09380fe106697