Migrate to pganalyze/pg_query_go

[johanbrandhorst]

It appears that @lfittl moved the pg_query_go repo to a new home in https://github.com/pganalyze/pg_query_go. Since sqlc builds much of its postgres capabilities on this library, we should aim to stay up to date with its development. This would also enable support for postgres 13 additions.

[lfittl]

@johanbrandhorst Thats right - note that the v2 release has considerable differences in the parse tree format (its now auto generated from Protocol Buffers), so be aware that this might be a small undertaking to update.

Happy to provide input if you or @kyleconroy have questions :)