add basic usb install support (see commit message).

transfers seems to work, although i have done very little testing.
i plan to extend the usb script so that it supports normal usb transfers, such as uploading and
downloading files to and from the switch.

however, most users are likely better off using mtp for said transfers.

the usb transfer code was taken from Haze, which is part of Atmosphere.

sphaira/include/ui/menus/usb_menu.hpp

@@ -0,0 +1,43 @@
+#pragma once
+
+#include "ui/menus/menu_base.hpp"
+#include "yati/source/usb.hpp"
+
+namespace sphaira::ui::menu::usb {
+
+enum class State {
+    // not connected.
+    None,
+    // just connected, starts the transfer.
+    Connected,
+    // set whilst transfer is in progress.
+    Progress,
+    // set when the transfer is finished.
+    Done,
+    // failed to connect.
+    Failed,
+};
+
+struct Menu final : MenuBase {
+    Menu();
+    ~Menu();
+
+    void Update(Controller* controller, TouchInfo* touch) override;
+    void Draw(NVGcontext* vg, Theme* theme) override;
+    void OnFocusGained() override;
+
+// this should be private
+// private:
+    std::shared_ptr<yati::source::Usb> m_usb_source{};
+    bool m_was_mtp_enabled{};
+
+    Thread m_thread{};
+    Mutex m_mutex{};
+    // the below are shared across threads, lock with the above mutex!
+    State m_state{State::None};
+    bool m_usb_has_connection{};
+    u32 m_usb_speed{};
+    u32 m_usb_count{};
+};
+
+} // namespace sphaira::ui::menu::usb