LibJS+LibWeb: Move JS::ModuleRequest to its own header file

This allows us to not include LibJS/AST.h in a couple more places.

Userland/Libraries/LibJS/Runtime/ModuleRequest.h

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2021-2022, David Tuin <davidot@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/FlyString.h>
+#include <AK/Vector.h>
+
+namespace JS {
+
+// 2.9 ModuleRequest Records, https://tc39.es/proposal-import-assertions/#sec-modulerequest-record
+struct ModuleRequest {
+    struct Assertion {
+        String key;
+        String value;
+    };
+
+    ModuleRequest() = default;
+
+    explicit ModuleRequest(FlyString specifier)
+        : module_specifier(move(specifier))
+    {
+    }
+
+    ModuleRequest(FlyString module_specifier, Vector<Assertion> assertions);
+
+    void add_assertion(String key, String value)
+    {
+        assertions.empend(move(key), move(value));
+    }
+
+    FlyString module_specifier;   // [[Specifier]]
+    Vector<Assertion> assertions; // [[Assertions]]
+};
+
+}