Provide tree display formatter (for Taxonomy terms and other trees with depth)

Problem/Motivation

Tree selects might have a dedicated UI, to solve cases like ✨ Javascript live-filter functionality for widget results (for large taxonomies) Needs review vice-versa.

The idea is to provide a good filter widget for tree structures, displaying the tree structure perfectly and allowing to expand / collapse etc.

Might be hard, if choices.js has no such support implemented.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes