Couchbase Lite : Support for string concatenation operator

This ticket is to track support for concat operator as described in n1ql : https://docs.couchbase.com/server/current/n1ql/n1ql-language-reference/stringops.html

This ticket is to track requests interest for this feature.

Reference :

https://forums.couchbase.com/t/like-query-on-concatenation-of-two-fields-in-couchbase-lite/19549

https://forums.couchbase.com/t/replicate-ifmissingornull-in-querybuilder/23759/4