Finding references for impl methods does not traverse usages via trait

[mkaput]

Repro:

#[derive(Drop)]
struct Foo {}

trait FooTrait {
    fn area(self: @Foo) -> u64;
}

impl FooImpl of FooTrait {
    fn are<caret>a(self: @Foo) -> u64 { 0 }
}

fn main() {
    let foo = Foo {};
    let x = foo.area();
}

This does not return foo.<sel>area</sel>().

Note that the expected outcome is to find all references to this implementation method. This means that if FooTrait would also be implemented for another struct, Bar, the usage bar.area() would not be picked up because it's not routed through FooImpl.

The same applies for alternative implementations of a same trait for same struct (say, FooImplBis).