Browser+LibWeb: Move cookie parser into LibWeb

This moves the cookie parsing steps out of CookieJar into their own file
inside LibWeb. It makes sense for the cookie structures to be in LibWeb
for a couple reasons:

1. There are some steps in the spec that will need to partially happen
   from LibWeb, such as the HttpOnly attribute.
2. Parsing the cookie string will be safer if it happens in the OOP tab
   rather than the main Browser process. Then if the parser blows up due
   to a malformed cookie, only that tab will be affected.
3. Cookies in general are a Web concept not specific to a browser.

Userland/Libraries/LibWeb/Forward.h

@@ -27,6 +27,10 @@
 
 #pragma once
 
+namespace Web::Cookie {
+struct ParsedCookie;
+}
+
 namespace Web::CSS {
 class CSSRule;
 class CSSImportRule;