LibURL/Pattern: Add a representation of a URL Pattern error

As the comment in this file explains the caller of LibURL APIs are
meant to assume if they see any error, that it is a TypeError since
that is all the spec throws at the moment.

A custom error type exists here so that we can include more
information in TypeError's which are thrown.

Libraries/LibURL/Pattern/PatternError.h

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2025, Shannon Booth <shannon@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Error.h>
+#include <AK/String.h>
+
+namespace URL::Pattern {
+
+// NOTE: All exceptions which are thrown by the URLPattern spec are TypeErrors which web-based callers are expected to assume.
+//       If this ever does not become the case, this should change to also include the error type.
+struct ErrorInfo {
+    String message;
+};
+
+template<typename ValueT>
+using PatternErrorOr = AK::ErrorOr<ValueT, ErrorInfo>;
+
+}