Auto merge of #94748 - tbu-:pr_file_arc, r=Amanieu

Add `Read`, `Write` and `Seek` impls for `Arc<File>` where appropriate

If `&T` implements these traits, `Arc<T>` has no reason not to do so
either. This is useful for operating system handles like `File` or
`TcpStream` which don't need a mutable reference to implement these
traits.

CC #53835.
CC #94744.

Author: bors