Show Trait instead of <Struct as Trait> in E0323

[estebank]

For a given file

trait Foo {
    fn bar(&self);
}

pub struct FooConstForMethod;

impl Foo for FooConstForMethod {
    const bar: u64 = 1;
}

show

error[E0323]: item `bar` is an associated const, which doesn't match its trait `Foo`

instead of

error[E0323]: item `bar` is an associated const, which doesn't match its trait `<FooConstForMethod as Foo>`

Fix #37618

[rust-highfive]

r? @arielb1

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[estebank]

/cc @nikomatsakis as per your comment in a previous PR

Not related to this PR, I think, but this text "<FooConstForMethod as Foo>" seems pretty funny to me; I expect to see just Foo... is there an open issue on that?

Now there is one and here's the fix.

[estebank]

r? @jonathandturner

[sophiajt]

Yeah, looks cleaner to me.

@bors r+ rollup

[bors]

📌 Commit 4226930 has been approved by jonathandturner