Add UHID_DESTROY control message

This message will be sent on gamepad disconnection.

Contrary to keyboard and mouse, which are registered once and are
unregistered when scrcpy exists, each gamepad is mapped with its own HID
id, and they can be plugged/unplugged dynamically.

app/src/control_msg.h

@@ -39,6 +39,7 @@ enum sc_control_msg_type {
     SC_CONTROL_MSG_TYPE_ROTATE_DEVICE,
     SC_CONTROL_MSG_TYPE_UHID_CREATE,
     SC_CONTROL_MSG_TYPE_UHID_INPUT,
+    SC_CONTROL_MSG_TYPE_UHID_DESTROY,
     SC_CONTROL_MSG_TYPE_OPEN_HARD_KEYBOARD_SETTINGS,
 };
 
@@ -105,6 +106,9 @@ struct sc_control_msg {
             uint16_t size;
             uint8_t data[SC_HID_MAX_SIZE];
         } uhid_input;
+        struct {
+            uint16_t id;
+        } uhid_destroy;
     };
 };