Lint unused assoc tys although the trait is used

[mu001999]

r? @pnkfelix

[mu001999]

 error: associated type `Bar` is never used --> library/core/tests/any.rs:137:14 | 136 | trait Foo { | --- associated type in this trait 137 | type Bar; | ^^^ | = note: `-D dead-code` implied by `-D warnings` = help: to override `-D warnings` add `#[allow(dead_code)]` 

the code is:

#[test] fn dyn_type_name() { trait Foo { type Bar; } assert_eq!( "dyn core::ops::function::Fn(i32, i32) -> i32", std::any::type_name::<dyn Fn(i32, i32) -> i32>() ); assert_eq!( "dyn coretests::any::dyn_type_name::Foo<Bar = i32> \  + core::marker::Send + core::marker::Sync", std::any::type_name::<dyn Foo<Bar = i32> + Send + Sync>() ); }

seems the assoc type is not marked live if it was used in the trait object.

[bors]

☔ The latest upstream changes (presumably #125443) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #128404) made this pull request unmergeable. Please resolve the merge conflicts.