Resolve "Display non-markdown content in the WYSIWYG mode of the SSE::Identifiers"

What does this MR do?

This MR prevents editing of markdown identifier syntax in WYSIWYG mode of the Static Site Editor. Example syntaxes are in the screenshots below, but the known variations in text form are in the code block below:

Normal:
- [identifier]: http://example1.com
- [multiple words]: http://example1.com
- [multiple words]: http://example1.com Also with a default title

Adjacent inline code:
- [`raw`]: http://example1.com/raw-file.md
- [some `raw` file]: http://example1.com/raw-file.md

Screenshots

Before	After

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Closes #221082 (closed)