Ad manual test to prove #4931 bug

tests/core/selection/manual/optimizationlist.html

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+<h2>Iframe editor</h2>
+<div id="editor1">
+	<ol>
+		<li>1</li>
+		<li>2
+		<ol>
+			<li>1</li>
+		</ol>
+		</li>
+		<li>&nbsp;</li>
+	</ol>
+
+</div>
+
+<h2>Divarea editor</h2>
+<div id="editor2">
+	<ol>
+		<li>1</li>
+		<li>2
+		<ol>
+			<li>1</li>
+		</ol>
+		</li>
+		<li>&nbsp;</li>
+	</ol>
+
+</div>
+
+<script>
+	if ( bender.tools.env.mobile ) {
+		bender.ignore();
+	}
+
+	CKEDITOR.replace( 'editor1' );
+
+	CKEDITOR.replace( 'editor2', {
+		extraPlugins: 'divarea',
+	} );
+</script>

tests/core/selection/manual/optimizationlist.md

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+@bender-tags: selection, 4.19.2, bug, 4931
+@bender-ui: collapsed
+@bender-ckeditor-plugins: wysiwygarea, toolbar, elementspath, sourcearea, list, undo, div, table, image, basicstyles, format
+
+
+1. Select entire content via `Ctrl+A`
+2. Delete content with backspace key.
+
+**Expected** The entire list is removed from the editor
+
+**Unexpected** There are list leftovers in the editor
+
+3. Repeat steps in the second editor