Search in associated items when type cannot be found

[estebank]

Given the following code:

rust/src/test/ui/associated-types/associated-types-eq-1.rs

Lines 4 to 11 in 1fb612b

	pub trait Foo {
	type A;
	fn boo(&self) -> <Self as Foo>::A;
	}
	fn foo2<I: Foo>(x: I) {
	let _: A = x.boo(); //~ ERROR cannot find type `A` in this scope
	}

we currently show

rust/src/test/ui/associated-types/associated-types-eq-1.stderr

Lines 1 to 7 in 1fb612b

	error[E0412]: cannot find type `A` in this scope
	--> $DIR/associated-types-eq-1.rs:10:12
	|
	LL | fn foo2<I: Foo>(x: I) {
	| - similarly named type parameter `I` defined here
	LL | let _: A = x.boo();
	| ^ help: a type parameter with a similar name exists: `I`

But the typo checks should also look at the associated types of all the locally accessible types and provide a reasonable suggestion.

In this specific case of assignment, we could also look at the type of boo for an appropriate type to supply.