LibWeb: Add the SubtleCrypto interface

Just some boilerplate code to get started :^)
This adds both the SubtleCrypto constructor to the window object, as
well as the crypto.subtle instance attribute.

Userland/Libraries/LibWeb/Crypto/SubtleCrypto.h

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2021, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/Bindings/Wrappable.h>
+
+namespace Web::Crypto {
+
+class SubtleCrypto
+    : public Bindings::Wrappable
+    , public RefCounted<SubtleCrypto> {
+public:
+    using WrapperType = Bindings::SubtleCryptoWrapper;
+
+    static NonnullRefPtr<SubtleCrypto> create()
+    {
+        return adopt_ref(*new SubtleCrypto());
+    }
+
+private:
+    SubtleCrypto() = default;
+};
+
+}
+
+namespace Web::Bindings {
+
+SubtleCryptoWrapper* wrap(JS::GlobalObject&, Crypto::SubtleCrypto&);
+
+}