impl blocks and struct definitions aren't counted as uses of a type alias

[cramertj]

The following code results in "warning: type alias is never used: Bar":

struct Foo;

type Bar = Foo;

struct MyStruct(Bar);

impl Bar {
    fn buzz() {}
}

fn main() {
    MyStruct(Foo);
    Foo::buzz();
}

[est31]

Dupe of #43123

[cramertj]

I'll add the extra case (struct definitions) to #43123 and close this.