feat(context): make parent public for invocation context

Some interceptors such as tracing need to add bindings to the parent,
which is typically the request context.

Author: raymondfeng

packages/context/src/__tests__/unit/invocation-context.unit.ts

@@ -43,6 +43,10 @@ describe('InvocationContext', () => {
     );
   });
 
+  it('has public access to parent context', () => {
+    expect(invocationCtxForGreet.parent).to.equal(ctx);
+  });
+
   it('throws error if method does not exist', () => {
     expect(() => invalidInvocationCtx.assertMethodExists()).to.throw(
       'Method MyController.prototype.invalid-method not found',

packages/context/src/interceptor.ts

@@ -60,7 +60,9 @@ export class InvocationContext extends Context {
    * @param args - An array of arguments
    */
   constructor(
-    parent: Context,
+    // Make `parent` public so that the interceptor can add bindings to
+    // the request context, for example, tracing id
+    public readonly parent: Context,
     public readonly target: object,
     public readonly methodName: string,
     public readonly args: InvocationArgs,