hooks: Allow field notation like the inline plugin

### Use case

As discussed in #3547 it would be greater if hooks could be provided with the same field notation that the inline plugin already supports.

This will make it easier to access `Item`-level attributes like `mtime` when the hook works on an `Album`.

Start by reading the discussion in #3547 and the inline plugin's existing field notation. Then trace how hooks receive items and determine the changes needed so hooks accept that notation and can access Item-level attributes such as mtime when operating on an Album.

Written by the indexing model from the issue text.