Bump ckeditor 43.1.1 => 43.3.1

Problem/Motivation

https://github.com/ckeditor/ckeditor5/releases/tag/v43.3.1

Steps to reproduce

Proposed resolution

Remaining tasks

Backport this to the gazillion current branches, TBD by the core committers.

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet