Prevent inline hardcoding width property using autogrow plugin

[KarolDawidziuk]

What is the purpose of this pull request?

Bug fix.

Does your PR contain necessary tests?

All patches that change the editor code must include tests. You can always read more
on PR testing,
how to set the testing environment and
how to create tests
in the official CKEditor documentation.

This PR contains

• Unit tests
• Manual tests

Did you follow the CKEditor 4 code style guide?

Your code should follow the guidelines from the CKEditor 4 code style guide which helps keep the entire codebase consistent.

• PR is consistent with the code style guide

What is the proposed changelog entry for this pull request?

* [#4891](https://github.com/ckeditor/ckeditor4/issues/4891): Fixed: [Autogrow](https://ckeditor.com/cke4/addon/autogrow) prevent impose fixed width size with single direction resize. 

What changes did you make?

Editor container shouldn't impose fixed size with single direction resize, so I've pass null as width parameter in editor.resize() method to prevent this.

Which issues does your PR resolve?

Closes #4891.

[sculpt0r]

Rebased on newest major.

[sculpt0r]

Nice job! It looks like the bug was introduced by... me 😞 in #4393

Also, your fix seems to be valid for the previous issue 😓

I think it will be good to change our docs for resize method since we can use type other than number or string - which is still valid usage of that method. Also, please look at my inline comments.

[KarolDawidziuk]

Thanks, @sculpt0r for the review.
I've added the changes that you mentioned and it's ready for another one.

[sculpt0r]

Rebase on newest major

[sculpt0r]

LGTM 🎉

However, I have to remove the comment about the height parameter. When you try to pass null there - the editor editable area is simply collapsed. There is no additional conditions for height value ;)