Another attempt to fix barrel.ts

This time, use an ambient `declare namespace` to declare the
`Ember.RSVP` types, which will avoid the ill-fated attempt to transpile
it at runtime using the babel typescript transform. The previous
implementation already required us to dynamically install the `RSVP`
property on the `Ember` object because the previous transpiler
infrastructure didn't reliably handle this situation, so this is
probably an improvement either way.

Author: wycats

packages/@ember/template-compiler/-internal-utils.ts

@@ -0,0 +1 @@
+export * from './lib/plugins/utils';

packages/@ember/template-compiler/package.json

@@ -5,6 +5,7 @@
     ".": "./index.ts",
     "./runtime": "./runtime.ts",
     "./-internal-primitives": "./-internal-primitives.ts",
+    "./-internal-utils": "./-internal-utils.ts",
     "./types": "./lib/types.ts"
   },
   "dependencies": {

packages/ember-template-compiler/lib/plugins/utils.ts

@@ -0,0 +1 @@
+export * from '@ember/template-compiler/-internal-utils';

packages/ember/barrel.ts

@@ -192,8 +192,6 @@ namespace Ember {
   export type ActionHandler = InternalActionHandler;
   export const Comparable = InternalComparable;
   export type Comparable = InternalComparable;
-  export const RSVP = _RSVP;
-  export type RSVP = typeof _RSVP;
 
   // ****@ember/-internals/view****
   export const ComponentLookup = views.ComponentLookup;
@@ -591,6 +589,20 @@ namespace Ember {
     | undefined;
 }
 
+// This syntax is not reliably implemented by TypeScript transpilers, but
+// we need to re-export the`RSVP` *namespace* for type compatibility.
+// To achieve this, we use a type-only `declare namespace` block to get the
+// types to behave correctly, and separately set the `RSVP` property on the
+// `Ember` object dynamically. (The types behave correctly because of
+// namespace merging semantics.)
+// eslint-disable-next-line @typescript-eslint/no-namespace
+declare namespace Ember {
+  // eslint-disable-next-line @typescript-eslint/no-unused-vars
+  export import RSVP = _RSVP;
+}
+
+Reflect.set(Ember, 'RSVP', _RSVP);
+
 interface EmberHandlebars {
   template: typeof template;
   Utils: {