Rollup merge of #93755 - ChayimFriedman2:allow-comparing-vecs-with-di…

…fferent-allocators, r=dtolnay

Allow comparing `Vec`s with different allocators using `==`

See https://stackoverflow.com/q/71021633/7884305.

I did not changed the `PartialOrd` impl too because it was not generic already (didn't support `Vec<T> <=> Vec<U> where T: PartialOrd<U>`).

Does it needs tests?

I don't think this will hurt type inference much because the default allocator is usually not inferred (`new()` specifies it directly, and even with other allocators, you pass the allocator to `new_in()` so the compiler usually knows the type).

I think this requires FCP since the impls are already stable.

library/alloc/src/vec/partial_eq.rs

@@ -20,7 +20,7 @@ macro_rules! __impl_slice_eq1 {
     }
 }
 
-__impl_slice_eq1! { [A: Allocator] Vec<T, A>, Vec<U, A>, #[stable(feature = "rust1", since = "1.0.0")] }
+__impl_slice_eq1! { [A1: Allocator, A2: Allocator] Vec<T, A1>, Vec<U, A2>, #[stable(feature = "rust1", since = "1.0.0")] }
 __impl_slice_eq1! { [A: Allocator] Vec<T, A>, &[U], #[stable(feature = "rust1", since = "1.0.0")] }
 __impl_slice_eq1! { [A: Allocator] Vec<T, A>, &mut [U], #[stable(feature = "rust1", since = "1.0.0")] }
 __impl_slice_eq1! { [A: Allocator] &[T], Vec<U, A>, #[stable(feature = "partialeq_vec_for_ref_slice", since = "1.46.0")] }