Investigate changing html layout for file tree

[ficristo]

Description

The current layout is composed with ul and li, plus there is some javascript that handle the selection of current folder and I think also the collapse/exapnd is done in js.
In #12047 I added some html to workaround a bug, which makes me think the layout can be improved.
Ideally we should delegate more operations to html and css.
If we go on this route it a possible breaking change.