Bugfix/types: Resolver extends EmberObject

Without this, it doesn't get exported as a class people can actually
instantiate with `Resolver.create()`.

(cherry picked from commit 67fc6c4)

index.d.ts

@@ -1,2 +1,4 @@
 import { Resolver as ResolverContract } from "@ember/owner";
+import EmberObject from "@ember/object";
+export default class Resolver extends EmberObject {}
 export default interface Resolver extends Required<ResolverContract> {}