Rollup merge of rust-lang#101569 - m-ou-se:alloc-no-rexport-argumentv1, r=thomcc

Don't re-export private/unstable ArgumentV1 from `alloc`.

The `alloc::fmt::ArgumentV1` re-export was marked as `#[stable]` even though the original `core::fmt::ArgumentV1` is `#[unstable]` (and `#[doc(hidden)]`).

(It wasn't usable though:

```
error[E0658]: use of unstable library feature 'fmt_internals': internal to format_args!
 --> src/main.rs:4:12
  |
4 |     let _: alloc::fmt::ArgumentV1 = todo!();
  |            ^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: add `#![feature(fmt_internals)]` to the crate attributes to enable
```
)

Part of rust-lang#99012

Author: Dylan-DPC

alloc/src/fmt.rs

@@ -558,7 +558,7 @@ pub use core::fmt::Alignment;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::fmt::Error;
 #[stable(feature = "rust1", since = "1.0.0")]
-pub use core::fmt::{write, ArgumentV1, Arguments};
+pub use core::fmt::{write, Arguments};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::fmt::{Binary, Octal};
 #[stable(feature = "rust1", since = "1.0.0")]