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.

packages/compiler-cli/integrationtest/tsconfig-build.json

@@ -4,7 +4,8 @@
     // in the same source directory with your code.
     "genDir": ".",
     "debug": true,
-    "enableSummariesForJit": true
+    "enableSummariesForJit": true,
+    "alwaysCompileGeneratedCode": true
   },
 
   "compilerOptions": {