Adding styles(basic BBCode?) support to TreeItem text

[Anutrix]

Currently, my project(a JSON viewer for large/massive JSON files) uses Tree and TreeItem. It serves really well from a logical and maintenance standpoint.

But I require making part of TreeItem's text bold or highlighted or change color for better UX.

Hi-jacking the draw behavior by setting cell_mode to CELL_MODE_CUSTOM with custom_draw and then using RichTextLabel with MOUSE_FILTER_IGNORE seems like an option but it will have heavy memory footprint by having full RichTextLabel nodes. Seems too hacky for long term maintenance anyways.

There seems to be some kinda-related issues for Tree both here and in main repo but wasn't sure which to track. Something like BBCode support in TreeItem text is practically what I require but I wasn't sure how best to put it in a proposal so started this discussion.