Docs: Synchronize and correct documentation for has_filter() and WP_Hook::has_filter().

`WP_Hook::has_filter()` returns true if `$function_to_check` is omitted and the hook being checked has one or more registered callbacks.

Follow-up to [49927].

See #51800.

git-svn-id: https://develop.svn.wordpress.org/trunk@49928 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-hook.php

@@ -187,14 +187,16 @@ final class WP_Hook implements Iterator, ArrayAccess {
 	/**
 	 * Checks if a specific action has been registered for this hook.
 	 *
-	 * When using the $function_to_check argument, this function may return a non-boolean value
-	 * that evaluates to false (e.g. 0), so use the === operator for testing the return value.
+	 * When using the `$function_to_check` argument, this function may return a non-boolean value
+	 * that evaluates to false (e.g. 0), so use the `===` operator for testing the return value.
 	 *
 	 * @since 4.7.0
 	 *
 	 * @param string         $tag               Optional. The name of the filter hook. Default empty.
 	 * @param callable|false $function_to_check Optional. The callback to check for. Default false.
-	 * @return false|int The priority of that hook is returned, or false if the function is not attached.
+	 * @return int|bool If `$function_to_check` is omitted, returns boolean for whether the hook has
+	 *                  anything registered. When checking a specific function, the priority of that
+	 *                  hook is returned, or false if the function is not attached.
 	 */
 	public function has_filter( $tag = '', $function_to_check = false ) {
 		if ( false === $function_to_check ) {