Add Dutch translation for "Show blocks" in ckeditor5_show_block

Problem/Motivation

The ckeditor5_show_block plugin currently does not provide a Dutch translation for the "Show blocks" label.

Steps to reproduce

• Install and configure the ckeditor5_show_block plugin.
• Set the CKEditor language to Dutch (nl).
• Observe that the "Show blocks" label is not translated.

Proposed resolution

Add the dutch translation for Show bloks ('Blokken weergeven')

Remaining tasks

User interface changes

API changes

Data model changes