t/85: Linking an image should not be possible

[oleq]

Suggested merge commit message (convention)

Fix: Linking an entire image should not be possible. Closes ckeditor/ckeditor5#4771.

[oskarwrobel]

Image should be added as a devDependency.

[Reinmar]

This change is bad because it couples image and link features. This should not happen this way. This should be managed through schema and checkAttributeInSelection(). So, unless there's some problem to control this through schema (in which case it must be mentioned in https://github.com/ckeditor/ckeditor5-engine/issues/532) this PR should be reverted.

[oleq]

When the ImageCaption is on, linking doesn't work because doc.schema.checkAttributeInSelection( doc.selection, 'linkHref' ) indeed returns false in a such situation like [<image></image>].

However, when ImageCaption is on, the following rules are added to the schema:

schema.registerItem( 'caption', '$block' );
schema.allow( { name: '$inline', inside: 'caption' } );
schema.allow( { name: 'caption', inside: 'image' } );

which make checkAttributeInSelection return true when

[<image><caption>a</caption></image>]

and false when

[<image><caption></caption></image>]

When there's a text in <caption>, it automatically means the linking is possible. I have no idea what to use to check if an attribute is allowed <image>here<caption>...</caption></image> instead of <image><caption>there</caption></image> for any selection. The first, shallow check would certainly solve the issue.

[Reinmar]

OK, I know what's wrong here, actually. It's checkAttributeInSelection(). And the issue is strongly related to https://github.com/ckeditor/ckeditor5-engine/issues/986. The same kind of fix is needed in checkAttributeInSelection(), but... this will disable not only link but also bold and italic. So, I'm not sure if we want to do that.

Let's revert this change and get back to the original ticket.