Detect stability attributes on methods

[huonw]

struct Foo;
impl Foo {
    #[deprecated]
    fn method(&self) {}
}

fn main() {
    Foo.method();
}

doesn't flag the use of method, since method calls are not in the def_map. As discussed in #8921, this will require passing the method_map from typeck into lint (or something along those lines).

(Part of #6875.)