Bundled Themes: Twenty Twenty HTML in featured image caption is being escaped.

Fixes the issue by replacing `esc_html` with `wp_kses_post` in the caption in featured images.

Props pierlo, JavierCasares, audrasjb.
Fixes #49833.
Built from https://develop.svn.wordpress.org/trunk@47940


git-svn-id: https://core.svn.wordpress.org/trunk@47713 1a063a9b-81f0-0310-95a4-ce76da25c4cd