[Rich text] List element tags aren't stripped out for the Rich Text Section's Heading Block

[kjellr]

Describe the current behavior

#1635 implemented a rich text control for the the Rich Text section's Heading block, and set it up to have its <p> tags replaced with <span> tags when it's rendered. The RTE recently added inline list functionality, which is not stripped out. This leads to a weird visual bug where we have giant large, misaligned bullets in the heading. (Related #2155)

Describe the expected behavior

The intent of this field is to have it behave like a single-line richtext field, so we should strip out the bullets for now.

In the longterm, this richtext field should eventually be replaced with a inline_richtext to prevent these sorts of issues in the future, but that comes with some compounding issues, so I'd recommend we just fix this specific bug for now.

Version information (Dawn, browsers and operating systems)

• Dawn Version: 7.0.1
• Chrome Version 108.0.5359.98
• macOS Version 13.0.1

Possible solution

Strip out ul and li tags.

Additional context/screenshots

[kjellr]

Closing because #2326 fixes this. 👍