[Style] style plugin assignment is not working properly

Problem/Motivation

We are using the style plugin to allow content editors to easily apply some classes for styling reasons. For example some buttons styles to an a tag:

a.btn.btn-primary|Primary Button
a.btn.btn-outline-primary|Primary Outline Button
a.btn.btn-secondary|Secondary Button

With CKE 4 it was possible to simply click on some part of the a tag and then select the style. Now with CKE5 this does not work anymore properly. Only if the whole link text is selected I can properly apply a style and the classes are added.

Steps to reproduce

- Use some stlyes in the editor, e.g:

a.btn.btn-primary|Primary Button
a.btn.btn-outline-primary|Primary Outline Button
a.btn.btn-secondary|Secondary Button

- Add some text via the edior
- add a link, have the curser on some parts of it (no selection)
- try to apply the "Primary Outline Button" style
- try to aplly a different style
- try to remove the style again

Proposed resolution

It should work as easily as with CKE 4

Remaining tasks

User interface changes

API changes

Data model changes

none

Release notes snippet