Update imports to match CKEditor 5 v46.

[Mati365]

This issue tracks the work needed to update imports to be compatible with CKEditor 5 version 46.

As part of the migration to the New Installation Methods (NIM), CKEditor is standardizing how public APIs are exposed. Many previously available imports (especially those relying on internal paths) are no longer accessible in v46.

To comply with the new structure:

• All public APIs should be imported from the package’s index.ts file.
• Some exports have been renamed to be more descriptive, unambiguous, and unique within the CKEditor 5 ecosystem.
• This introduces breaking changes that require adjusting import paths and symbol names accordingly.

More context here: https://github.com/ckeditor/ckeditor5/issues/18583

[Mati365]

I see we use mix and DataApiMixin which was removed in https://github.com/ckeditor/ckeditor5/issues/18584. We need to adjust it.