Add validation for usage of unwrap() on DOM elements

[ravijayaramappa]

Before LWC GA, dom elements were being wrapped in a proxy. unwrap() was a way to peel away the proxy and access the native element. Post GA, lwc has stopped wrapping elements in a proxy. So the unwrap() call is basically a no-op and waste of CPU cycles.

Add an eslint rule to flag usages of unwrap() on dom elements.

[pmdartus]

Since it's not something that is exposed to the platform. I feel reluctant about adding such linting rule here. I will close this issue, for now, @ravijayaramappa feel free to reopen the issue if you think it's something we really need to pursue.