Support changing substitution plugins on a matcher without having to re-enter content

Updating the version this relates to as 6.1.x, and changing the priority to "Major," as this is a blocker for more gracefully resolving ✨ Decoupled website - absolute URL Active .

I've updated the approach suggested above to work with the latest version of the module (6.1.x). This works with CKEditor 5, as well as with the Linkit field widget/formatter. However, in reviewing this approach, I think it still has one major drawback: in the context of the text format filter (i.e., CKEditor) this change will not allow existing site content to be updated to use a different substitution, derived from the matcher. This is because the implementation relies on knowing what the data-entity-matcher is, and this would not be present in existing data. Since the Linkit field formatter, on the other hand, can find the matcher associated with the selected Linkit Profile, it *can* make previously entered data updated.

What would need to be possible in order to dynamically derive the currently-associated Substitution plugin from the Matcher would be the ability to find what Drupal text format is executing the filter (since that would have information about which Linkit Profile is used, which would give the Matcher, which would give the Substitution plugin. I don't believe there's a way to access that information at the right point in the rendering process for text format filters.

So, I'm not optimistic about introducing this change, as I think we want something that will support existing content.

I've posted the updated patch anyway, in case it prompts ideas from the community.