FEATURE: Automatically include Ember's own types

- In TS, add an `import 'ember-source/types'` statement.
- In JS, add a `/** @typedef {import('ember-source/types')} */` comment.

blueprints/addon/files/local-types/index.ts

@@ -0,0 +1,12 @@
+<% if (typescript) { %>
+// This "side-effect"-type import provides auto-complete, go-to-def, etc. for
+// Ember's internals throughout your application, so don't remove it!
+import 'ember-source/types';
+<% } else { %>
+// This "type definition" import comment provides auto-complete, go-to-def, etc.
+// for Ember's internals throughout your application, so don't remove it, even
+// if you do not use TypeScript at all.
+/**
+  @typedef {import('ember-source/types')} Types
+*/
+<% } %>

blueprints/app/files/app/app.ts

@@ -10,3 +10,15 @@ export default class App extends Application {
 }
 
 loadInitializers(App, config.modulePrefix);
+
+<% if (typescript) { %>
+// This "side-effect"-type import provides auto-complete, go-to-def, etc. for
+// Ember's internals throughout your application, so don't remove it!
+import 'ember-source/types';
+<% } else { %>
+// This "type definition" import comment provides auto-complete, go-to-def, etc.
+// for Ember's internals throughout your application, so don't remove it!
+/**
+  @typedef {import('ember-source/types')} Types
+*/
+<% } %>