Postgres 13: Query string in planner methods

Postgres 13 is now passing query string to planner methods and we have it in distributed_planner, we might possibly get rid of some deparsing if we can find a way to replace table names with shard names in the given query string.

Start at the distributed_planner entry point and inspect how PostgreSQL 13 passes the query string to planner methods. Determine whether table names can be replaced with shard names in that query without the current deparsing, and define a demonstrable result for any viable approach.

Written by the indexing model from the issue text.