General: Replace substr_compare() usage in the str_ends_with() polyfill.

This avoids a warning on PHP < 7.2.18 if haystack is an empty string:
{{{
Warning: substr_compare(): The start position cannot exceed initial string length
}}}

Follow-up to [52040], [55158], [55990], [56014].

See #58220.

git-svn-id: https://develop.svn.wordpress.org/trunk@56015 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/compat.php

@@ -488,7 +488,7 @@ if ( ! function_exists( 'str_ends_with' ) ) {
 
 		$len = strlen( $needle );
 
-		return 0 === substr_compare( $haystack, $needle, -$len, $len );
+		return $needle === substr( $haystack, -$len, $len );
 	}
 }