From thinking about it and merely looking at the gif example... I think you could actually get there via language server alone - at least mostly?

It just highlights parts that interface with a symbol, right? And that's information the language server is supposed to expose.

You'd "just" have to make a x+1 mapping to highlight anything that's touching the symbol

To be clear, I'm just speculating here and not speaking with authority on the topic. It's possible I'm missing something which makes this approach infeasible in practice