Refactor the Procedures namespace

### Problem Statement

Blockly has a `Procedures` namespace, which is basically a catch-all for a bunch of procedure-related utilties, many of which aren't actually general-purpose. It would be nice to clean this up to shrink our public API.

### Proposed Solution

See: https://docs.google.com/document/d/1n4MxZQu49mniC7aUtZ1X4xvwWgpL3st4aDU25pwdaNc/edit#heading=h.o948m9ldldol