add php_unescape_html_entities() proto to the header

(fixes #39665)

Author: tony2001

ext/standard/html.h

@@ -38,5 +38,6 @@ PHP_FUNCTION(html_entity_decode);
 PHP_FUNCTION(get_html_translation_table);
 
 PHPAPI char *php_escape_html_entities(unsigned char *old, int oldlen, int *newlen, int all, int quote_style, char *hint_charset TSRMLS_DC);
+PHPAPI char *php_unescape_html_entities(unsigned char *old, int oldlen, int *newlen, int all, int quote_style, char *hint_charset TSRMLS_DC);
 
 #endif /* HTML_H */