Allow forcing polyfill and not crashing when web components polyfills are forced

[e111077]

Since Chrome extensions do not allow for creating Web Components, we recommend our users force the custom elements polyfill. The issue is that if your elements are using the polyfill on a browser that supports elementInternals, you get an error that you are attaching ElementInternals to a non-custom element. In these cases it would be great to have a flag to force the CE polyfill or a way for users to invoke it without the checks.