Preserve empty inline elements

[dsdon]

📝 Provide detailed reproduction steps (if any)

CKEditor4 uses an empty anchor element as the destination for a document/bookmark link. CKEditor5 removes the empty anchor element.

1. In Source view, type <a id="footnotes" name="footnotes"></a>
2. Switch back to WYSIWYG view, then switch back to Source view.

✔️ Expected result

Preserve the empty anchor element

❌ Actual result

The empty anchor element is removed.

📃 Other details

This appeared to be fixed in Issue#: 9888 but seems to be broken again.
I was able to duplicate this in the "Source code editing and HTML support" demo.
I also tried this using an empty span tag and had the same results so I assume this applies to all empty inline elements that have opening/closing tags.

• Browser: Chrome Version: 131.0.6778.71
• OS: Windows 11
• First affected CKEditor version: 43.2.0
• Installed CKEditor plugins: …
  import {
  ClassicEditor,
  AccessibilityHelp,
  Alignment,
  Autoformat,
  AutoImage,
  AutoLink,
  Autosave,
  BlockQuote,
  Bold,
  CloudServices,
  Code,
  CodeBlock,
  Essentials,
  FindAndReplace,
  FontBackgroundColor,
  FontColor,
  FontFamily,
  FontSize,
  GeneralHtmlSupport,
  Heading,
  Highlight,
  HorizontalLine,
  HtmlComment,
  HtmlEmbed,
  ImageBlock,
  ImageCaption,
  ImageInline,
  ImageInsertViaUrl,
  ImageResize,
  ImageStyle,
  ImageTextAlternative,
  ImageToolbar,
  ImageUpload,
  Indent,
  IndentBlock,
  Italic,
  Link,
  LinkImage,
  List,
  ListProperties,
  MediaEmbed,
  PageBreak,
  Paragraph,
  PasteFromOffice,
  RemoveFormat,
  SelectAll,
  ShowBlocks,
  SourceEditing,
  SpecialCharacters,
  SpecialCharactersArrows,
  SpecialCharactersCurrency,
  SpecialCharactersEssentials,
  SpecialCharactersLatin,
  SpecialCharactersMathematical,
  SpecialCharactersText,
  Strikethrough,
  Style,
  Subscript,
  Superscript,
  Table,
  TableCaption,
  TableCellProperties,
  TableColumnResize,
  TableProperties,
  TableToolbar,
  TextPartLanguage,
  TextTransformation,
  // Title,
  Underline,
  Undo
  } from 'ckeditor5';

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[Witoso]

Bookmarks feature will be available in the next release (#1944). Meanwhile, to preserve empty elements, you need to configure GeneralHtmlSupport with the allowEmpty property.