Merge #6401

6401: Only show `self` ident when showing parameter self hints r=matklad a=Veykril

This just hints all self parameters with the `self` token, this is therefor equal to how all other parameters are displayed, but given the self param special in how its defined in a function signature it might make sense to keep the `&`/`&mut` parts as well as emitting those tokens for explict `Self` types that are taken by ref like `self: &Rc<Self>`?

Fixes #6400

Co-authored-by: Lukas Wirth <lukastw97@gmail.com>