[DocsUI M3] Add navigation rail layout for medium size screen

* Add a new layout nav_rail_layout for medium size >=600 && <900
  which also uses DrawerLayout but adds a narrower sidebar with
  icon/label only.
* Reuse RootsFragment to render Navigation rail so we can keep
  all existing functionality for navigation drawer on navigation
  rail. We store the layout ID on the RootsFragment argument to
  distinguish which layout is rendering, in medium size layout,
  2 instances of RootsFragment will be rendered: one for the
  navigation drawer, the other for navigation rail.
* A new layout nav_rail_item_root is created to cater the layout
  for navigation rail items.
* Extend the existing navigation drawer item classes to create
  the corresponding navigation rail item classes so we can use
  different layout for navigation rail items.

Check the bug item for demo.

Bug: 381958615
Test: Manual inpsection
Flag: com.android.documentsui.flags.use_material3
Change-Id: I8fac4646031e248020755327caed6b427b5d08cf