Introduce ambient type definitions

Ultimately we'd like to convert the package to TS, but this unblocks
wider ecosystem adoption of the stable/preview Ember types. This PR can
also serve as a model for other packages which want to publish types in
a similar way.

This will also work just fine with the `@types` packages from
DefinitelyTyped once [a key PR][pr] lands there, but that is not the
path we will recommend, so this only includes the `ember-source` peer
dependency.

[pr]: DefinitelyTyped/DefinitelyTyped#63589

(cherry picked from commit 3907d48)

# Conflicts:
#	addon/package.json
#	package-lock.json
#	test-app/package.json

index.d.ts

@@ -0,0 +1,2 @@
+import { Resolver as ResolverContract } from "@ember/owner";
+export default interface Resolver extends Required<ResolverContract> {}

package.json

@@ -9,6 +9,7 @@
   "bugs": {
     "url": "https://github.com/ember-cli/ember-resolver/issues"
   },
+  "types": "index.d.ts",
   "repository": {
     "type": "git",
     "url": "git+https://github.com/ember-cli/ember-resolver.git"

tests/dummy/app/app.js

@@ -1,7 +1,7 @@
-import Application from '@ember/application';
-import Resolver from './resolver';
-import loadInitializers from 'ember-load-initializers';
-import config from './config/environment';
+import Application from "@ember/application";
+import Resolver from "./resolver";
+import loadInitializers from "ember-load-initializers";
+import config from "./config/environment";
 
 export default class App extends Application {
   modulePrefix = config.modulePrefix;
@@ -10,3 +10,10 @@ export default class App extends Application {
 }
 
 loadInitializers(App, config.modulePrefix);
+
+// Makes Ember's type definitions visible throughout the project, thereby using
+// TS to power autocomplete for all Ember types in any editor.
+/**
+ * @typedef {import('ember-source/types')} Stable
+ * @typedef {import('ember-source/types/preview')} Preview
+ */