MB-16181: Transfer the collection name over DCP

MB-16181: Transfer the collection name over DCP

The DCP mutation/deletion callbacks now take a collection_len field,
the data in this field will be sent over DCP streams when a client
has signalled they want collection-aware DCP.

For example "dairy::cheese" will set a collection length of 5,
default collection documents, set a collection length of 0.

Change-Id: I303d9b18bc5d0fd0968708d84e461ee59577c003
Reviewed-on: http://review.couchbase.org/78135
Reviewed-by: Dave Rigby <daver@couchbase.com>
Tested-by: Build Bot <build@couchbase.com>