LSP: Don't find node on function call, do find node on assignment, find node when de-structuring

[lucasavila00]

It's more what the Rust LSP does...

I constantly mis-hover a function argument, and the LSP shows the call. I constantly try to create a variable and hover it to inspect the type, but the assignment does not has hover.

This MR fixes both.

Is find_node used for important stuff or can it be changed to please the LSP UX?

[lpil]

Is find_node used for important stuff or can it be changed to please the LSP UX?

It's only used by LSP and is safe to change. The LSP is pretty basic and rough currently :)