title: Make crate visible methods of `OverlayedChanges` public.

doc:
  - audience: Node Dev
    description: | 
      Make some methods of `OverlayedChanges` namely `set_child_storage`, `clear_child_storage`, `clear_prefix` 
      and `clear_child_prefix` public which only had crate level visibility.

migrations:
  db: []

  runtime: []

crates:
  - name: sp-state-machine

host_functions: []