Clipboard+LibGUI: Make set_clipboard_data asynchronous

There's no need for GUI applications to block after the clipping is
already in flight.

Userland/Libraries/LibGUI/Clipboard.cpp

@@ -75,7 +75,7 @@ void Clipboard::set_data(ReadonlyBytes data, const String& type, const HashMap<S
     if (!data.is_empty())
         memcpy(buffer.data<void>(), data.data(), data.size());
 
-    connection().set_clipboard_data(move(buffer), type, metadata);
+    connection().async_set_clipboard_data(move(buffer), type, metadata);
 }
 
 void ClipboardServerConnection::clipboard_data_changed(String const& mime_type)

Userland/Services/Clipboard/ClipboardServer.ipc

@@ -3,5 +3,5 @@ endpoint ClipboardServer
     greet() => ()
 
     get_clipboard_data() => (Core::AnonymousBuffer data, [UTF8] String mime_type, IPC::Dictionary metadata)
-    set_clipboard_data(Core::AnonymousBuffer data, [UTF8] String mime_type, IPC::Dictionary metadata) => ()
+    set_clipboard_data(Core::AnonymousBuffer data, [UTF8] String mime_type, IPC::Dictionary metadata) =|
 }