Everywhere: Replace a bundle of dbg with dbgln.

These changes are arbitrarily divided into multiple commits to make it
easier to find potentially introduced bugs with git bisect.Everything:

The modifications in this commit were automatically made using the
following command:

    find . -name '*.cpp' -exec sed -i -E 's/dbg\(\) << ("[^"{]*");/dbgln\(\1\);/' {} \;

Services/Clipboard/main.cpp

@@ -58,7 +58,7 @@ int main(int, char**)
     server->on_ready_to_accept = [&] {
         auto client_socket = server->accept();
         if (!client_socket) {
-            dbg() << "Clipboard: accept failed.";
+            dbgln("Clipboard: accept failed.");
             return;
         }
         static int s_next_client_id = 0;