Support undotted-self for this param closure

[A4-Tacks]

Using this instead of self in a closure is a common pattern

Example

struct Foo { field: i32 }
impl Foo {
    fn foo(&mut self) {
        let f: fn(&mut Self) = |this| { $0 };
        f(self)
    }
}

Before this PR

fd self.field           i32
me self.foo() fn(&mut self)
lc self            &mut Foo
lc this            &mut Foo
md core
sp Self                 Foo
st Foo                  Foo
tt Fn
tt FnMut
tt FnOnce
bt u32                  u32

After this PR

fd this.field           i32
me this.foo() fn(&mut self)
lc self            &mut Foo
lc this            &mut Foo
md core
sp Self                 Foo
st Foo                  Foo
tt Fn
tt FnMut
tt FnOnce
bt u32                  u32

[ChayimFriedman2]

Thanks, this is nice!

[ChayimFriedman2]

I wonder, when this is used this is usually because using self will be an error (usually a borrowck error), so perhaps we should punish self's rank a bit in this case, to nudge users towards this?

[A4-Tacks]

I am not familiar with ranking related codes.

Is it implemented on the client-side extension or the LSP server?

[ChayimFriedman2]

In the server,

rust-analyzer/crates/ide-completion/src/item.rs

Line 265 in b21e738

pub fn score(self) -> u32 {

[A4-Tacks]

If self has a special ranking, it may be feasible to make this score higher