SDL_hidapi_steamdeck: report touch controller events

Previously, touchpad events were not reported to the application.
This patch exposes two touchpads and forwards x/y/pressure information
from the HIDAPI packet.

This fixes issue #12855

src/joystick/hidapi/SDL_hidapi_steamdeck.c

@@ -233,6 +233,18 @@ static void HIDAPI_DriverSteamDeck_HandleState(SDL_HIDAPI_Device *device,
     values[1] = (pInReport->payload.deckState.sAccelZ / 32768.0f) * 2.0f * SDL_STANDARD_GRAVITY;
     values[2] = (-pInReport->payload.deckState.sAccelY / 32768.0f) * 2.0f * SDL_STANDARD_GRAVITY;
     SDL_SendJoystickSensor(timestamp, joystick, SDL_SENSOR_ACCEL, ctx->sensor_timestamp_us, values, 3);
+
+    SDL_SendJoystickTouchpad(timestamp, joystick, 0, 0,
+            pInReport->payload.deckState.sPressurePadLeft > 0,
+            pInReport->payload.deckState.sLeftPadX        / 65536.0f + 0.5f,
+            pInReport->payload.deckState.sLeftPadY        / 65536.0f + 0.5f,
+            pInReport->payload.deckState.sPressurePadLeft / 32768.0f);
+
+    SDL_SendJoystickTouchpad(timestamp, joystick, 1, 0,
+            pInReport->payload.deckState.sPressurePadRight > 0,
+            pInReport->payload.deckState.sRightPadX        / 65536.0f + 0.5f,
+            pInReport->payload.deckState.sRightPadY        / 65536.0f + 0.5f,
+            pInReport->payload.deckState.sPressurePadRight / 32768.0f);
 }
 
 /*****************************************************************************************************/
@@ -366,6 +378,9 @@ static bool HIDAPI_DriverSteamDeck_OpenJoystick(SDL_HIDAPI_Device *device, SDL_J
     SDL_PrivateJoystickAddSensor(joystick, SDL_SENSOR_GYRO, update_rate_in_hz);
     SDL_PrivateJoystickAddSensor(joystick, SDL_SENSOR_ACCEL, update_rate_in_hz);
 
+    SDL_PrivateJoystickAddTouchpad(joystick, 1);
+    SDL_PrivateJoystickAddTouchpad(joystick, 1);
+
     return true;
 }