6665: Support self in reference search r=matklad a=Veykril
The approach here is simply checking the descendants of the function body for `PathExpr` then checking whether it only contains a single `self` `PathSegment`, this is to prevent us from picking up `self` tokens from local `UseTree`s.
Co-authored-by: Lukas Wirth <lukastw97@gmail.com>
ac30710ada