Instead of using the namespace which is hardcoded we use the tag name that was
used to register the element (or the "real" tag name in case of a scoped element).

This way if AppShell is regsitered as "dbp-some-app" it can still be overriden by
specifying "dbp-some-app" in the overrides object.

Create a new instance with createInstance() and call setOverrides()
with override data to override translations.

See the tests for some examples.

This has proper support for rollup while providing the same API.

This is what open-wc recommends now and uses in their @open-wc/testing package