dm vdo: implement top-level deduplication index

The top-level deduplication index brings all the earlier components
together. The top-level index creates the separate zone structures that
enable the index to handle several requests in parallel, handles
dispatching requests to the right zones and components, and coordinates
metadata to ensure that it remain consistent. It also coordinates recovery
in the event of an unexpected index failure.

If sparse caching is enabled, the top-level index also handles the
coordination required by the sparse chapter index cache, which (unlike most
index structures) is shared among all zones.

Co-developed-by: J. corwin Coburn <corwin@hurlbutnet.net>
Signed-off-by: J. corwin Coburn <corwin@hurlbutnet.net>
Co-developed-by: Michael Sclafani <dm-devel@lists.linux.dev>
Signed-off-by: Michael Sclafani <dm-devel@lists.linux.dev>
Co-developed-by: Thomas Jaskiewicz <tom@jaskiewicz.us>
Signed-off-by: Thomas Jaskiewicz <tom@jaskiewicz.us>
Co-developed-by: Bruce Johnston <bjohnsto@redhat.com>
Signed-off-by: Bruce Johnston <bjohnsto@redhat.com>
Signed-off-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>