show what closing }s belong to for longer functions

[matthiaskrgr]

I've had a couple of situations already where I would have liked RA to print something to identify what function/method a closing } belongs to.

This could look like this

impl HasSource for Field {
    type Ast = FieldSource;
    fn source(self, db: &dyn HirDatabase) -> Option<InFile<Self::Ast>> {
        let var = VariantId::from(self.parent);
        let src = var.child_source(db.upcast());
        let field_source = src.map(|it| match it[self.id].clone() {
            Either::Left(it) => FieldSource::Pos(it),
            Either::Right(it) => FieldSource::Named(it),
        });
        Some(field_source)
    } <fn source(self, &dyn HirDatabase)>
} <impl HasSource for Field>

This makes it easier to navigate code when functions are very long and users won't have to scroll up to the function body to check what the } belongs to.

The <..> text would be greyed out.

[matklad]

cc @SomeoneToIgnore

this also in theory a job for breadcrumbs, but I like the inlay hints angle