build(docs-infra): turn on disableTypeScriptVersionCheck in angularCompilerOptions (#27536)

We need to do this because we don't yet have a released version of angular
with typescript 3.2 support and on CI we test both against the snapshot and
whatever is in aio/yarn.lock.

Once we have the next rc or a stable relase we should be able to remove
this flag.

PS: I also removed the preserveWhitespace:false because that's the default now.

PR Close #27536

aio/src/tsconfig.app.json

@@ -14,6 +14,6 @@
     "**/*.spec.ts"
   ],
   "angularCompilerOptions": {
-    "preserveWhitespaces": false
+    "disableTypeScriptVersionCheck": true
   }
-}
+}