Allowed icon pack not enforced in editor

Problem/Motivation

When adding icon selection on a text format, if set a limitation on pack list, the selector is limited but the embed icon can be manually altered and set a non allowed pack, it will display properly when it should not be allowed.

Steps to reproduce

Enable ui_icons_test to have some packs.

• Edit a text format with CKEditor
• Add icon widget and 'embed icon'
• Limit to one or multiple packs, for example test_path

• Create a content with this text format
• Click the icon, use autocomplete, the selection is properly limited to test_path
• Insert icon

• Switch to source
• Edit the icon id and set test_svg:foo
• Switch back to editor
• The icon is displayed when it should not
• Save
• The icon is displayed, it should not