Editor: Correctly indent definition lists when switching from the visual to the text editor.

Props ocean90, katieburch.
Fixes #23299.
Built from https://develop.svn.wordpress.org/trunk@35999


git-svn-id: https://core.svn.wordpress.org/trunk@35964 1a063a9b-81f0-0310-95a4-ce76da25c4cd