AK: Add a type alias for DistinctNumeric's underlying type

Author: https://github.com/trflynn89
Commit: 60b56892ca
Pull-request: https://github.com/SerenityOS/serenity/pull/17111
Reviewed-by: https://github.com/AtkinsSJ ✅
Reviewed-by: https://github.com/bgianfo ✅

AK/DistinctNumeric.h

@@ -89,6 +89,8 @@ class DistinctNumeric {
     constexpr static Option options { Opts()... };
 
 public:
+    using Type = T;
+
     constexpr DistinctNumeric() = default;
 
     constexpr DistinctNumeric(T value)