This is a bug, but the mixin just ignored undefined here.
The next version will be stricter and raises an error in this case.

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

See the tests for some examples.

Uses a separate namespace that gets used over the default one, so we can override,
but also remove the overrides again when needed.

This has the problem that all clones have the same store, so this overrides
the translations for all clones and not just the one providing the overrides.

In newer versions there is now a normal method for this which also supports
dynamically added components.

The static version is deprecated and removed in 2.0, so we need to port here.

Include the highlight.js css in all activities and move the
code css into the app, so it's defined where it is used.

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