Transform proconfig for faster execution.

Transform proconfig for faster execution.

Store function config settings in lists to avoid the need to parse and
allocate for each function execution.

Speedup is modest but significant. Additionally, this change also
seems cleaner and supports some other performance improvements under
discussion.

Discussion: https://postgr.es/m/04c8592dbd694e4114a3ed87139a7a04e4363030[email protected]
Reviewed-by: Nathan Bossart