docs: add comment markers for internal goog.define replacement (#32795)

This is needed for closure to properly tree-shake ngDevMode and ngI18nClosureMode.

PR Close #32795

packages/core/src/util/ng_dev_mode.ts

@@ -8,6 +8,9 @@
 
 import {global} from './global';
 
+// Do not remove: needed for closure to be able to properly tree-shake ngDevMode.
+// goog.define
+
 declare global {
   /**
    * Values of ngDevMode

packages/core/src/util/ng_i18n_closure_mode.ts

@@ -8,6 +8,9 @@
 
 import {global} from './global';
 
+// Do not remove: needed for closure to be able to properly tree-shake ngI18nClosureMode.
+// goog.define
+
 declare global {
   const ngI18nClosureMode: boolean;
 }