LibWeb: Add a helper class to work around empty execution context stack

We've peppered this workaround around the code base as needed in a few
different ways. This adds a helper class to perform this workaround in
order to simplify doing so, and ensure cleanup occurs in a RAII fashion.
This also makes it easier to grep for places where this workaround is
employed.

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -363,6 +363,7 @@ set(SOURCES
     HTML/Scripting/ModuleMap.cpp
     HTML/Scripting/ModuleScript.cpp
     HTML/Scripting/Script.cpp
+    HTML/Scripting/TemporaryExecutionContext.cpp
     HTML/Scripting/WindowEnvironmentSettingsObject.cpp
     HTML/SessionHistoryEntry.cpp
     HTML/SharedImageRequest.cpp

Userland/Libraries/LibWeb/HTML/Scripting/TemporaryExecutionContext.cpp

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2023, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/HTML/Scripting/Environments.h>
+#include <LibWeb/HTML/Scripting/TemporaryExecutionContext.h>
+
+namespace Web::HTML {
+
+TemporaryExecutionContext::TemporaryExecutionContext(EnvironmentSettingsObject& environment_settings)
+    : m_environment_settings(environment_settings)
+{
+    m_environment_settings.prepare_to_run_script();
+}
+
+TemporaryExecutionContext::~TemporaryExecutionContext()
+{
+    m_environment_settings.clean_up_after_running_script();
+}
+
+}

Userland/Libraries/LibWeb/HTML/Scripting/TemporaryExecutionContext.h

@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2023, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/Forward.h>
+
+namespace Web::HTML {
+
+// When JS is run from outside the context of any user script, we currently do not have a running execution context.
+// This results in a crash when we access VM::running_execution_context(). This is a spec issue. Until it is resolved,
+// this is a workaround to temporarily push an execution context.
+class TemporaryExecutionContext {
+public:
+    explicit TemporaryExecutionContext(EnvironmentSettingsObject&);
+    ~TemporaryExecutionContext();
+
+private:
+    EnvironmentSettingsObject& m_environment_settings;
+};
+
+}