Post Title: return no markup if title is empty

[carolinan]

Description

If a post has an empty title, then the Post Title block should not return any markup.
Closes #35224

How has this been tested?

1. Create a post or page without a title
2. Add a post title block
3. View the front and confirm that there is no markup for the empty title block.
4. Add a title to the item and confirm that it still works correctly.

Screenshots

Twenty Twenty Two, single post without title:

Types of changes

Enhancement

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[Mamaduka]

Thanks, @carolinan. It works great!