merge doublemelon (#2067)

non-exhaustive (but exhausting) list of changes:

* base laid for multiple window support, but will likely require more work to work correctly
* encapsulation of frontend state for proper multi-instance support
* (JIT still needs a fix for the NDS::Current workaround but we can get there later)
* new, more flexible configuration system

src/frontend/qt_sdl/Net.h

@@ -0,0 +1,43 @@
+/*
+    Copyright 2016-2023 melonDS team
+
+    This file is part of melonDS.
+
+    melonDS is free software: you can redistribute it and/or modify it under
+    the terms of the GNU General Public License as published by the Free
+    Software Foundation, either version 3 of the License, or (at your option)
+    any later version.
+
+    melonDS is distributed in the hope that it will be useful, but WITHOUT ANY
+    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+    FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with melonDS. If not, see http://www.gnu.org/licenses/.
+*/
+
+#ifndef NET_H
+#define NET_H
+
+#include "types.h"
+#include "Net_PCap.h"
+#include "Net_Slirp.h"
+
+namespace Net
+{
+using namespace melonDS;
+
+bool Init();
+void DeInit();
+
+void RegisterInstance(int inst);
+void UnregisterInstance(int inst);
+
+void RXEnqueue(const void* buf, int len);
+
+int SendPacket(u8* data, int len, int inst);
+int RecvPacket(u8* data, int inst);
+
+}
+
+#endif // NET_H