AK: Use StringView as its own peek type

StringView is already a reference type, and copying it is cheap, so we
should use it as its own peek type.

AK/StringView.h

@@ -388,6 +388,8 @@ private:
 
 template<>
 struct Traits<StringView> : public DefaultTraits<StringView> {
+    using PeekType = StringView;
+    using ConstPeekType = StringView;
     static unsigned hash(StringView s) { return s.hash(); }
 };