Support for row values comparisons

Hi, I'm trying to do something like below to implement keyset pagination

> SELECT * FROM contacts
> WHERE (lastname,firstname) > (?1,?2)
> ORDER BY lastname, firstname
> LIMIT 7;

(from https://www.sqlite.org/rowvalue.html#scrolling_window_queries)

What I basically need is an operator that allows comparing n-tuple columns to n-tuple values. Is there going to be a support for this? I actually wrote my own operators but if you guys can officially support this for types Pair(col1, col2) and Triple(col1, col2, col3) that'll be amazing.

No source files or tests are named. Start by reviewing Exposed's existing comparison operators and the SQLite row-value example linked in the issue, then determine how Pair and Triple column/value comparisons should be represented and tested. Done means n-tuple comparisons support keyset-pagination predicates such as (lastname, firstname) > (?1, ?2).

Written by the indexing model from the issue text.