Bug 14645429: Part 2 - Add infrastructure for defining named services exposed to JS. r=mccr8

This builds on the existing static components infrastructure to allow defining
a Services.jsm-type services cache with no runtime memory overhead for any
services until they're accessed.

Any class entry with a 'js_name' attribute automatically becomes available on
the services cache with that name, and any interfaces listed in its
'interfaces' list are automatically queried on it.

Differential Revision: https://phabricator.services.mozilla.com/D81417