Move libusb utilities to LibusbUtils

* Simplifies libusb context usage and allows us to set options for
all contexts easily. Notably, this lets us enable usbdk support
in libusb, which is now opt-in in the latest version.

* Moves the libusb config descriptor wrapper class to LibusbUtils too
since that could easily be reused.

* Moves device listing to LibusbUtils too and add a lock around it
as some libusb backends are not thread safe.

* Consequences: only a single context and a single event handling
thread is used now, which is more efficient.

Source/Core/Core/LibusbUtils.h

@@ -0,0 +1,48 @@
+// Copyright 2019 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <functional>
+#include <memory>
+
+#include "Common/CommonTypes.h"
+
+struct libusb_config_descriptor;
+struct libusb_context;
+struct libusb_device;
+
+namespace LibusbUtils
+{
+template <typename T>
+using UniquePtr = std::unique_ptr<T, void (*)(T*)>;
+
+// Return false to stop iterating the device list.
+using GetDeviceListCallback = std::function<bool(libusb_device* device)>;
+
+class Context
+{
+public:
+  Context();
+  ~Context();
+
+  operator libusb_context*() const;
+  bool IsValid() const;
+
+  // Only valid if the context is valid.
+  bool GetDeviceList(GetDeviceListCallback callback);
+
+private:
+  class Impl;
+  std::unique_ptr<Impl> m_impl;
+};
+
+// Use this to get a libusb context. Do *not* use any other context
+// because some libusb backends such as UsbDk only work properly with a single context.
+// Additionally, device lists must be retrieved using GetDeviceList for thread safety reasons.
+Context& GetContext();
+
+using ConfigDescriptor = UniquePtr<libusb_config_descriptor>;
+ConfigDescriptor MakeConfigDescriptor(libusb_device* device, u8 config_num = 0);
+}  // namespace LibusbUtils