Allow resolving index.* modules with non-.js file extensions. #10027
As reported by @justinanastos via Slack, files with non-
Fixing this involves updating both the runtime module system and our build-time
Unfortunately this fix will have to wait for the next Meteor release, since it involves changes to the build tool.
The previous commit enabled importing index.* modules at runtime, but unfortunately the build-time Resolver logic also needed updating, which will require a new Meteor release.