Add classList methods polyfill for Opera Mini

The support for IE11 has been dropped → since Drupal 10.0.x. Furthermore Safari does support all methods of classList since version 7. So meanwhile the polyfill is only needed for Opera Mini (see supported browsers → and browser support for classList). I've updated the issue title and summary accordingly.

The last patch does include the polyfill for IE11 and Safari and therefore needs work (maybe just alter comments).

So meanwhile the polyfill is only needed for Opera Mini

According to #3202818: Remove untrue declaration of Opera Mini (in reverse proxy mode) support from Drupal 9.3 → , Opera Mini in 'High Data Savings' mode should work as well as Opera Mobile and "Can I Use" say classList feature is supported on Opera Mobile.
Opera Mini in 'Extreme Data Savings' mode had been dropped support since Drupal 9.3.

I think no need to take further action for this issue.

Thanks all for confirming this is no longer needed.