Add a method for `ARef` that is analogous to `Arc::into_raw`. It is the
inverse operation of `ARef::from_raw`, and allows you to convert the
`ARef` back into a raw pointer while retaining ownership of the
refcount.
This new function will be used by [1] for converting the type in an
`ARef` using `ARef::from_raw(ARef::into_raw(me).cast())`. The author has
also needed the same function for other use-cases in the past, but [1]
is the first to go upstream.
Link: https://lore.kernel.org/r/20240801-vma-v3-1-db6c1c0afda9@xxxxxxxxxx [1]
Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>