refactor(compiler): don’t always compile .ngfactory.ts files by default

This puts the behavior introduced in 573b8611bc behind the new flag
`alwaysCompileGeneratedCode` to not break users that might have relied
on this behavior.

integration/hello_world__closure/tsconfig.json

@@ -1,7 +1,8 @@
 {
   "angularCompilerOptions": {
     "annotationsAs": "static fields",
-    "annotateForClosureCompiler": true
+    "annotateForClosureCompiler": true,
+    "alwaysCompileGeneratedCode": true
   },
 
   "compilerOptions": {