Draft: PoC for file-tree extension in Source Editor

What does this MR do and why?

Describe in detail what your merge request does and why.

Screenshots or screen recordings

Creating new file in repo's root
1 level down in the tree
2 levels down in the tree
Editing a file deep in the tree

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #388957