LibJS: Do not use the $ special character in file names

The dollar sign is a special character in POSIX shells and in the Ninja
build file format. If the file name contains a `$`, something goes wrong
in the escaping/unescaping of this symbol, and CMake/GCC/Clang generate
invalid dependency files where not all instances of `$` are escaped
properly. Because of this, Ninja fails to rebuild `$262Object.cpp` if
the headers included by it have changed.

Stale `$262Object.cpp.o` files have been the cause of mysterious crashes
multiple times which only go away after doing a clean build. Let's
prevent these from happening again by removing the `$` from the
filename.

Userland/Libraries/LibJS/Contrib/Test262/262Object.h

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2021, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibJS/Contrib/Test262/AgentObject.h>
+#include <LibJS/Contrib/Test262/IsHTMLDDA.h>
+#include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/Object.h>
+
+namespace JS::Test262 {
+
+class $262Object final : public Object {
+    JS_OBJECT($262Object, Object);
+
+public:
+    virtual ThrowCompletionOr<void> initialize(Realm&) override;
+    virtual ~$262Object() override = default;
+
+private:
+    explicit $262Object(Realm&);
+
+    virtual void visit_edges(Visitor&) override;
+
+    GCPtr<AgentObject> m_agent;
+    GCPtr<IsHTMLDDA> m_is_htmldda;
+
+    JS_DECLARE_NATIVE_FUNCTION(clear_kept_objects);
+    JS_DECLARE_NATIVE_FUNCTION(create_realm);
+    JS_DECLARE_NATIVE_FUNCTION(detach_array_buffer);
+    JS_DECLARE_NATIVE_FUNCTION(eval_script);
+};
+
+}