Cover the anchors a format without the Anchor button must keep

Problem/Motivation

#3619043: Scope the CKEditor 5 plugin wiring to the editors that use the Anchor button fixed a Major defect: the module altered the Arbitrary HTML Support plugin definition globally, so a format that never enabled the Anchor button lost the id and name attributes off its anchors the moment the editor loaded, and saving destroyed them.

The fix is covered by a unit test over the plugin definition shape, but nothing in the functional suite exercises the behaviour itself. The suite only ever drives a format that has the Anchor button, so the regression could come back without a single test failing.

Proposed resolution

• Add a second format to the test recipe, No Anchor Test: CKEditor 5, General HTML Support (no filter_html), and a toolbar with no Anchor button.
• Add a scenario that writes <a id> and <a name> into that format, asserts both survive the editor, saves, and asserts the id is in the rendered page.
• Make the format-switch step wait for an instance other than the one it replaced, instead of waiting for the Anchor plugin. A format under test may deliberately lack that plugin, so the plugin-specific wait cannot serve this scenario - and telling the new instance from the outgoing one is the more accurate fix for the race it was written for.

Remaining tasks

• ✅ File an issue
• ✅ Addition/Change/Update/Fix
• ✅ Testing to ensure no regression
• ✅ Automated unit/functional testing coverage
• ➖ Developer Documentation support
• ➖ User Guide Documentation support
• ➖ UX/UI designer responsibilities
• ➖ Accessibility and Readability
• ❌ Reviewed by a human
• ❌ Code review by maintainers
• ✅ Full testing and approval
• ✅ Credit contributors
• ✅ Review with the product owner
• ✅ Update Release Notes
• ✅ Release

User interface changes

• N/A

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• N/A