LibThread: Introduce a new threading library

This library is meant to provide C++-style wrappers over lower
level APIs such as syscalls and pthread_* functions, as well as
utilities for easily running pieces of logic on different
threads.

Libraries/LibThread/Thread.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include <AK/Function.h>
+#include <LibCore/CObject.h>
+
+namespace LibThread {
+
+class Thread final : public CObject {
+    C_OBJECT(Thread);
+
+public:
+    explicit Thread(Function<int()> action);
+    virtual ~Thread();
+
+    void start();
+    void quit(int code = 0);
+
+private:
+    Function<int()> m_action;
+    int m_tid { -1 };
+};
+
+}