object_safe_for_dispatch: auto trait bounds

[lcnr]

#![feature(object_safe_for_dispatch)]
trait Trait {
    fn not_object_safe() {}
}

fn impls_send<T: Send + ?Sized>() {}

fn main() {
    impls_send::<dyn Trait + Send>();
}

passes with the old solver, but results in an error with new:

error[E0277]: `dyn Trait + Send` cannot be sent between threads safely
  --> <source>:10:18
   |
10 |     impls_send::<dyn Trait + Send>();
   |                  ^^^^^^^^^^^^^^^^ `dyn Trait + Send` cannot be sent between threads safely
   |
   = help: the trait `Send` is not implemented for `dyn Trait + Send`
note: required by a bound in `impls_send`
  --> <source>:7:18
   |
7  | fn impls_send<T: Send + ?Sized>() {}
   |                  ^^^^ required by this bound in `impls_send`

unsure whether this is desired or not, it does not match the old solver. Caused by https://github.com/rust-lang/rust/blob/bdc15928c8119a86d15e2946cb54851264607842/compiler/rustc_trait_selection/src/solve/assembly/mod.rs#L793-L795