MB-10817: Add JSON_checker as a separate library

Change-Id: I6cfc71e09d9e643ffa986feb038efa5a6c5579ad
Reviewed-on: http://review.couchbase.org/35547
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>