Cookie path may contain forbidde character

[sgrekhov]

The following test fails now

import "dart:io";
import "../../../Utils/expect.dart";

main() {
  Cookie cookie = new Cookie.fromSetCookieValue(" cname = cval; path= / ");
  Expect.equals("/", cookie.path);
  Expect.throws(() {cookie.path = " /a/b/c:/; ";});
}

According to the RFC-6265

path-value = <any CHAR except CTLs or ";">

Therefore " /a/b/c:/; " is not a valid value for the path because it contains forbidden character ;
Tested on Dart SDK version: 2.10.0-0.0.dev (dev) (Wed Jul 22 19:58:38 2020 +0200) on "windows_x64"

[a-siva]

/cc @zichangg