AK: Add Eternal<T> and use it in various places.

This is useful for static locals that never need to be destroyed:

Thing& Thing::the()
{
    static Eternal<Thing> the;
    return the;
}

The object will be allocated in data segment memory and will never have
its destructor invoked.

LibGUI/GClipboard.cpp

@@ -3,19 +3,7 @@
 #include <WindowServer/WSAPITypes.h>
 #include <LibC/SharedBuffer.h>
 
-GClipboard& GClipboard::the()
-{
-    static GClipboard* s_the;
-    if (!s_the)
-        s_the = new GClipboard;
-    return *s_the;
-}
-
-GClipboard::GClipboard()
-{
-}
-
-String GClipboard::data() const
+String GClipboard::data()
 {
     WSAPI_ClientMessage request;
     request.type = WSAPI_ClientMessage::Type::GetClipboardContents;