Self-closing tags with trailing slash in CKEditor 4

Introduced additional test case for CKEditor 4 version, since we support both D9 and D10 I need to make a version comparison to not run CKEditor 4 test in D10 since the module is not in place. I had to rename the helper functions in order to introduce the same helper functions for CKEditor4.

I pushed the test that should fail without the fix. In the next commit I will push the fix and test should pass.

For some reason the JS alert doesn't produce exception over drupal CI. On my local I have the test failing as expected.

I pushed the fix that will prevent the removal of the actual html tag since we already prevent self-closing tags to be added to the open_tags stack in JS. This caused to remove the opening html tag due to a self-closing tag that was detected based on "/>" characters before we handled self-closing tags based on an array list, resulting in the alter message.

I've tested the merge request and can confirm it works as expected. Assigning to Heather to do a final code review.

Tested & reviewed, looks good to go!

Thank you!

Automatically closed - issue fixed for 2 weeks with no activity.