addBuiltIn method
Adds the module make makes to the built-ins the editor brings
(ModuleRegistry.builtIns), ahead of every other module, and
rebuilds the registries — for a scope made before its host knew of
it. Nothing happens when one with that id is there already.
Implementation
void addBuiltIn(EditorModule Function(EditorScope scope) make) =>
_addBuiltIn(make);