[rpcsx-os] fork: implement vm and vfs fork

stub metadbg device
implement notification device
implement sys_pipe

orbis-kernel/include/orbis/pipe.hpp

@@ -0,0 +1,13 @@
+#pragma once
+
+#include "KernelAllocator.hpp"
+#include "file.hpp"
+#include "utils/Rc.hpp"
+
+namespace orbis {
+struct Pipe final : File {
+  kvector<std::byte> data;
+};
+
+Ref<Pipe> createPipe();
+} // namespace orbis