AK+Format: Accept unsigned long in replacement fields.

I ran into this exact but at least twenty times in Serenity alone. The
C++ Standard dictates that 'unsigned long' and 'unsigned long long' are
distinct types even though on most platforms they are usually both 64
bit integers.

Also it wasn't possible to evaluate IsIntegral<T> for types that were
not integers since it used MakeUnsigned<T> internally.

AK/StdLibExtras.h

@@ -326,6 +326,7 @@ constexpr T&& forward(typename RemoveReference<T>::Type&& param) noexcept
 
 template<typename T>
 struct MakeUnsigned {
+    using Type = void;
 };
 template<>
 struct MakeUnsigned<signed char> {
@@ -507,6 +508,9 @@ using Void = void;
 template<typename... _Ignored>
 constexpr auto DependentFalse = false;
 
+template<typename T>
+using IsUnsigned = IsSame<T, MakeUnsigned<T>>;
+
 }
 
 using AK::AddConst;