(new-types-package-org-2) Make builtin mapping stuff a top-level submodule
Summary:
Since this orchestrates between dagster.config and soon-to-be
dagster.core.types, but this at the top-level
Depends on D1821
Test Plan: BK
Reviewers: alangenfeld, max
Reviewed By: alangenfeld
Differential Revision: https://dagster.phacility.com/D1822