Rollup merge of rust-lang#99317 - yanchith:borrow-vec-ta-as-slice-t, r=Mark-Simulacrum

Borrow Vec<T, A> as [T]

Hello all,

When `Vec` was parametrized with `A`, the `Borrow` impls were omitted and currently `Vec<T, A>` can't be borrowed as `[T]`. This PR fixes that.

This was probably missed, because the `Borrow` impls are in a different file - `src/alloc/slice.rs`.

We briefly discussed this here: rust-lang/wg-allocators#96 and I was told to go ahead and make a PR :)

I tested this by building the toolchain and building my code that needed the `Borrow` impl against it, but let me know if I should add any tests to this PR.

Author: matthiaskrgr

library/alloc/src/slice.rs

@@ -836,14 +836,14 @@ impl<T: Clone, V: Borrow<[T]>> Join<&[T]> for [V] {
 ////////////////////////////////////////////////////////////////////////////////
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Borrow<[T]> for Vec<T> {
+impl<T, A: Allocator> Borrow<[T]> for Vec<T, A> {
     fn borrow(&self) -> &[T] {
         &self[..]
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> BorrowMut<[T]> for Vec<T> {
+impl<T, A: Allocator> BorrowMut<[T]> for Vec<T, A> {
     fn borrow_mut(&mut self) -> &mut [T] {
         &mut self[..]
     }