fix(compiler): compile .ngfactory.ts files even if nobody references them. (#16899)

This is especially important for library authors, as they will
not reference the .ngfactory.ts files.

Fixes #16741

integration/hello_world__closure/tsconfig.json

@@ -13,7 +13,8 @@
     "noImplicitAny": false,
     "sourceMap": false,
     "experimentalDecorators": true,
-    "outDir": "built/src",
+    "outDir": "built",
+    "rootDir": ".",
     "declaration": true,
     "types": []
   },