Styling inside FAQ Block causes titles to break

[timofey-drozhzhin]

• I've read and understood the contribution guidelines.
• I've searched for any related issues and avoided creating a duplicate issue.

Please give us a description of what happened.

Whenever bold text is pasted into FAQ Block title, it pastes <strong> tags inside <strong> tags, breaking titles. It's not html5 valid to have <strong> tags inside <strong> tag.
This issue may be in some ways related to #17221.

Please describe what you expected to happen and why.

Text pasted inside FAQ Block titles should be stripped of html, especially for <strong> tags, since the titles are already wrapped inside <strong> tags.

How can we reproduce this behavior?

1. Copy bold text (wrapped in <strong>) from either a Google Document or a web page.
2. Paste text inside Yoast FAQ Block title.
3. Publish the page and examine the generated HTML.

Technical info

• If relevant, which editor is affected (or editors):

• Classic Editor
• Gutenberg
• Classic Editor plugin

• Which browser is affected (or browsers):

• Chrome
• Firefox
• Safari
• Other

Used versions

• WordPress version: 5.7.2
• Yoast SEO version: 16.7 Premium
• Gutenberg plugin version:
• Classic Editor plugin version:
• Relevant plugins in case of a bug:

• Tested with theme:

[Djennez]

I feel that between #17221 , #11802 and #11801 this is pretty much covered. So to prevent too many duplicate / related issues, I am closing this as a duplicate.