bbPress: emojis causing stray img tags to display

Emojis are sometimes causing closing `` tags to appear in the WP.org forums.

Live example:

https://wordpress.org/support/topic/front-page-74/#post-16371055

I also did some testing on the test site, adding emojis in three different ways. Here's the thread:

https://test.wordpress.org/support/topic/emoji-test/

Related: https://github.com/Automattic/blocks-everywhere/issues/111

Reproduce the stray closing img tags using the live WordPress.org example and the three emoji insertion methods in the linked test thread. Compare the resulting rendered markup and trace the relevant emoji handling in the blocks-everywhere integration; done means emojis render without displaying stray img tags in forum posts.

Written by the indexing model from the issue text.