PostgreSQL array functions support

I was looking to use `array_position` so that I could query based on a list of keys and return the first/last match in that list, but it seems like all the stuff in https://www.postgresql.org/docs/current/functions-array.html would be useful to define in the PostgreSQL module.

Start with the PostgreSQL array functions documentation linked in the issue, especially array_position, and inspect the repository's PostgreSQL module. Determine which array functions should be exposed and how they fit the existing module; done means the requested PostgreSQL array support is defined and usable.

Written by the indexing model from the issue text.