feat: Prevent empty wrapper divs for about sections with no content

[PKulkoRaccoonGang]

Description

Added a content check before rendering the xblock. If the about section is empty or contains only whitespace, return an empty string instead of rendering the xblock.

Useful information to include:

• html_block.py
• xblock_utils/init.py
• xblock_wrapper.html
• Slack conversation

Supporting information

Empty about_sidebar_html (and other about sections) were generating unnecessary xblock wrapper divs even when they contained no content, causing extra DOM elements and potential styling issues.

Initial setup

Go to openedx/frontend-app-catalog#38 and follow all the steps to set up and run the new Catalog MFE.

Testing instructions

1. Open the new Catalog MFE Course About page and the Schedule and Details page.
2. Add any content to the Course About Sidebar HTML section and save it.
3. Verify that the content is displayed correctly on both the updated MFE page and the legacy page.
4. Make sure the content is wrapped in the xblock wrapper.
5. Go back to the Schedule and Details page and remove the content from the Course About Sidebar HTML section.
6. Confirm that the about_sidebar_html field returns an empty string without xblock stuff.

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[ormsbee]

I've noticed that if you delete everything in the HTML editor for the course overview, it still leaves <p>&nbsp;</p>. It might be worth special casing this to be equivalent to blank.

[PKulkoRaccoonGang]

Thanks for catching that! I’ve added an is_empty_html function to handle cases with empty tags that might get saved on the frontend.

I also think this should ideally be validated on the Authoring MFE side. I’m planning to open a separate issue for that.

[ormsbee]

We'll want to check out APM traces of this on the sandbox after it lands just to make sure the HTML parsing isn't getting too expensive on an endpoint that will likely get hit a lot. I honestly don't expect this to be a problem--just something to keep in the back of our minds.