It looks like the only use of jQuery UI in CodeEditor is the resizable plugin to make the editor resizable: https://github.com/wikimedia/mediawiki-extensions-CodeEditor/blob/156c035c3e7ca52d098aa10e2b171e10de5499ea/modules/jquery.codeEditor.js#L411-L418

@Samwilson @MusikAnimal @TheresNoTime Can't ResizingDragBar in Realtime Preview be repurposed for this?

Yep! Now that Realtime Preview is enabled by default, we can (soon; let's give it a few weeks or something) set WikiEditor to have RTP by default, and then (because CM already requires WikiEditor) we can just remove the Resizable plugin usage from CodeMirror. (I could've sworn I already added this comment to this ticket a few weeks ago! I guess not though.)

Then CM will have the full-width resize bar at the bottom, and not the "corner triangle that looks like it's a two-dimensional resizer but actually is just up-and down" one. And get rid of the legacy code, and the special handling that adds both the new and old. :)

Reminder that this still needs to happen.

Code for the new resized is located outside of this extension, in the wikieditor module ext.wikiEditor.realtimepreview
Not sure if that one can be required without introducing side effects. We might have to make it available as a separate module ?

var ResizingDragBar = require( './ResizingDragBar.js' );

	// Add the resizing bar.
	var bottomDragBar = new ResizingDragBar( { isEW: false } );
	$uiText.after( bottomDragBar.$element );

then hook into: ext.WikiEditor.realtimepreview.resize for the resize event.

Untagging from MediaWiki-Interface in core as this is not itself a task about the jquery.ui module that core ships, and thus not actionable from that perspective (the parent task is). This is a task for CodeEditor component about its use of the jquery.ui module provided by core.