process_read_dir doesn't give control over recursive state propagation

[g2p]

I would like to pass state from one ReadDir to the next.
I don't mind if it's ReadDirState or DirEntryState.

At the moment, I'm limited between passing the same state to all child directories (via ReadDirState), or I can pass state to all children (via DirEntry::client_state), but the entry or its state won't be accessible in the next process_read_dir call.

When using process_read_dir, I have access to the previous DirEntryState (cloned from the parent), and I can update it, but all ReadDir calls built from children will share the same ReadDirState, and I need to make them distinct.

I see two ways to fix this:

• add an entry argument to the process_read_dir closure, replacing the current depth and path arguments with a DirEntry. Depth, path, client_state, file_type… can all be accessed on the entry.
• split the children argument to the closure into yield_children and recurse_children (elements can appear on either or both). recurse_children should be a Vec<RecEntry> with RecEntry containing at least a path and a ReadDirState.