Adding view image caption if not present when insertion to model caption is made

[szymonkups]

Suggested merge commit message (convention)

Fix: Adding view image caption if not present when insertion to model caption is made. Closes ckeditor/ckeditor5#5068.

[Reinmar]

R- for 3 reasons:

1. There's no integration test with undo, so it's hard to understand whether the original issue was indeed fixed.
2. There are too many functions exposed in imagecaption/utils. Some of them have really low value, like isInsideCaption() or insertViewCaptionAndBind(). Please remember that these utils make a public API, so whatever lands there should have some sense. Also, isInsideCaption() and insertViewCaptionAndBind() are now used in just one file and are very specific. The other utils may not be super needed now, but they are very generic and encapsulate some logic: isCaption(), getCaptionFromImage().
3. You didn't explain how the code works and I can see that it works differently than what we discussed in #58.

[szymonkups]

1. You're right, I will add it.
2. I've moved those methods to utilities because in my opinion the main file was unnecessarily growing. I also wanted to have separate tests for those specific methods. On the other hand, I can agree that when we treat utils as a public API some of the functions don't have much sense in other contexts.
3. The essential change is adding insertMissingViewCaptionElement method to insert event listener. It does what you proposed in that thread:

Perhaps a solution would be to listen on conversion's insert event and if insert happens inside model's <caption>, then adding the <figcaption> in the view too. Am I right?

[Reinmar]

The essential change is adding insertMissingViewCaptionElement method to insert event listener. It does what you proposed in that thread:

Hm... I missed it in the code. Sorry.

I've moved those methods to utilities because in my opinion the main file was unnecessarily growing. I also wanted to have separate tests for those specific methods. On the other hand, I can agree that when we treat utils as a public API some of the functions don't have much sense in other contexts.

There's nothing wrong with long files as long as the code inside is written nicely. In fact, it's often easier to read the code if it's in one place than when it's split between multiple locations. Developers tend to over-optimise this because it's a typical evidence of premature optimisation. This leads to futher complication because exposed code creates public API and should be written in a more future-proof way.

imagecaptionengine has ~250LOC which is still a very short module, so feel free to drop there more code.