Comments: Strip html tags from comment content before blacklist_keys comparison.
Use wp_kses() to clean comment_content for preg_match against the blacklist_keys. Also includes some initial unit tests for wp_blacklist_check().
Previously, if a blacklisted key was used in comment_content split by an html tag the regex in wp_blacklist_check() would not find a match. Example: Where "springfield" was a blacklisted word, if the content of a comment included spring<i>field</i>" wp_blacklist_check()` would not return true.
Props cfinke.
Fixes #37208.