LibWebView+LibCore: Manage process lifecycle using a SIGCHLD handler

This large commit also refactors LibWebView's process handling to use
a top-level Application class that uses a new WebView::Process class to
encapsulate the IPC-centric nature of each helper process.

Userland/Libraries/LibWebView/Process.cpp

@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2024, Andrew Kaster <akaster@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibCore/Process.h>
+#include <LibWebView/Process.h>
+
+namespace WebView {
+
+Process::Process(ProcessType type, RefPtr<IPC::ConnectionBase> connection, Core::Process process)
+    : m_process(move(process))
+    , m_type(type)
+    , m_connection(move(connection))
+{
+}
+
+Process::~Process()
+{
+    if (m_connection)
+        m_connection->shutdown();
+}
+
+}