fix(compiler): ignore calls to unresolved symbols in metadata (#15970)

This only shows up in the language service. Calls to symbols
that are not resolve resulted in null instead of being resolved
causing the language service to see exceptions when the null
was not expected such as in the animations array.

Fixes #15969

packages/compiler/src/aot/static_reflector.ts

@@ -601,7 +601,7 @@ export class StaticReflector implements ɵReflectorReader {
               case 'ignore':
                 return expression;
             }
-            return null;
+            return IGNORE;
           }
           return mapStringMap(expression, (value, name) => simplify(value));
         }