Formatting: fix wpautop() to stop adding paragraph tags around <figcaption>.

Fixes #39307 for trunk.
Built from https://develop.svn.wordpress.org/trunk@39912


git-svn-id: http://core.svn.wordpress.org/trunk@39849 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/formatting.php

@@ -506,6 +506,12 @@ function wpautop( $pee, $br = true ) {
 		$pee = preg_replace( '%\s*(<(?:source|track)[^>]*>)\s*%', '$1', $pee );
 	}
 
+	// Collapse line breaks before and after <figcaption> elements.
+	if ( strpos( $pee, '<figcaption' ) !== false ) {
+		$pee = preg_replace( '|\s*(<figcaption[^>]*>)|', '$1', $pee );
+		$pee = preg_replace( '|</figcaption>\s*|', '</figcaption>', $pee );
+	}
+
 	// Remove more than two contiguous line breaks.
 	$pee = preg_replace("/\n\n+/", "\n\n", $pee);