Data submitted in the forms demo contains unnecessary whitespace characters

[Dumluregn]

Are you reporting a feature request or a bug?

Bug

Provide detailed reproduction steps (if any)

1. Go to https://ckeditor.com/docs/ckeditor4/latest/examples/angular.html#/forms
2. Create a list
3. Submit the form
4. Examine exported data

Expected result

Data that is reusable in the editor is sent.

Actual result

We submit the data with whitespace characters like \n and \t added by htmlwriter. We should remove them to submit the data that can actually be reused in the editor.

The issue occurs in both docs and integration sample and has to be fixed independently.