t/311: createListDropdown helper should use clickOutsideHandler

[oleq]

Suggested merge commit message (convention)

Other: The createListDropdown helper should use clickOutsideHandler. Closes ckeditor/ckeditor5#5410.

[oleq]

self.r-: This change breaks this test
https://github.com/ckeditor/ckeditor5-heading/blob/888f9571528f78720c231c19b2358fd5e02f7397/tests/heading.js#L93-L96 as the clickOutsideHandler references view#element before Template.extend in https://github.com/ckeditor/ckeditor5-heading/blob/master/src/heading.js#L98-L106.

Again, it's all about https://github.com/ckeditor/ckeditor5-ui/issues/262 :(

[oleq]

It turned out this code still won't work.

It's because the clickOutsideHandler requires a reference to View#element in its contextElements, which is not available in the createListDropdown helper because it returns an instance which is not rendered (yet). And it makes sense, because one might want to customize the instance even further so we cannot simply render() it in createListDropdown.

Possible solutions:

1. Implement View#render event fired after the view is rendered. Then:

   function createListDropdown( ... ) {
   	const dropdownView = createDropdown( ... );
   
   	// ...
   
   	dropdownView.on( 'render', () => {
   		clickOutsideHandler( {
   			emitter: dropdownView,
   			activator: () => dropdownView.isOpen,
   			callback: () => {
   				dropdownView.isOpen = false;
   			},
   			contextElements: [ dropdownView.element ]
   		} );
   	} );
   
   	// ...
   }

2. Allow contextElements defined as function, so it returns the value (dropdownView.element) on demand when the actual mousedown is fired and, obviously, the dropdownView.element already exists.

[Reinmar]

The #render event sound fine, as something you'd want anyway in some other place.

[Reinmar]

Actually, sorry – #rendered because it should be fired once the element is already available (plus, there won't be a conflict with the method name).

[oleq]

I decorated View#render method instead. Seems like the easiest solution.

[oleq]

Due to recent changes in the drop-down API, this PR became obsolete. Replaced by #353.