Watchdog causes memory leaks

[pomek]

☝️ Most probably the watchdog feature causes it. Whenever a new instance is created, the old reference is not destroyed (

ckeditor5-react/src/ckeditor.jsx

Lines 91 to 95 in f271c49

	if ( this.context instanceof ContextWatchdog ) {
	this.watchdog = new EditorWatchdogAdapter( this.context );
	} else {
	this.watchdog = new EditorWatchdog( this.editor );
	}

).

Originally posted by @pomek in ckeditor/ckeditor5#8725 (comment)

[pomek]

I've copied the memory leak test from CKEditor 5 and, fortunately, I wasn't right. The component destroys all references correctly. The test is here: 0d74194.