iov_iter: Provide copy_folio_from_iter()

Provide a copy_folio_from_iter() wrapper.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Alexander Viro <viro@zeniv.linux.org.uk>
cc: Christian Brauner <christian@brauner.io>
cc: Matthew Wilcox <willy@infradead.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/20240814203850.2240469-14-dhowells@redhat.com/

 # v2
Signed-off-by: Christian Brauner <brauner@kernel.org>