Detect stability attributes on methods

``` rust
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.)
