Add an option to orient motion controls for a handheld

[elpendor]

Closes #3871.

SDL reports gamepad motion in the frame of a controller lying face up, which is how a DualShock is held — so passing event->gsensor.data straight through is correct for one. A handheld is held upright instead, and its frame is 90 degrees away about X. X is left-right in both, so pitch arrives correctly while yaw and roll land on each other: tilting the device moves the camera, turning it does nothing. On a Steam Deck a real 90 degree yaw arrives as -89.1 on z against +23.5 on y.

Input.motion_controls_vertical rotates motion -90 degrees about X — (x, y, z) to (x, -z, y) — before it reaches the emulated pad. Gyro and accelerometer both, since they share the frame. Per-game overrideable like the other input settings.

Off by default, and not auto-detected: nothing SDL reports says how a device is being held, and the rotation is wrong for a controller resting face up.

Built and run on a Steam Deck (OLED) in a retail game with motion controls. Off, behaviour is unchanged; on, a 90 degree yaw reads 92.0 about true vertical and the camera turns with the device.

No GUI checkbox here — config and per-game overrides only. Happy to add one to the Qt settings dialog if that is wanted.

[kalaposfos13]

You can save an unnecessary copy of this buffer by inlining this logic into GameController::UpdateGyro, replacing the memcpy there.

[elpendor]

Done — the transform now writes straight into gyro_buf/accel_buf, so the stack buffer is gone.

One thing it ran into: input_mouse.cpp's EmulateGyro calls both functions too, with values already in the frame a game expects (a constant (0, 9.81, 0) accel and mouse deltas mapped to pitch/yaw). Rotating those would break mouse gyro whenever the option is on, so the functions take a device_frame flag defaulting to false, and only sdl_window.cpp passes true.

Also added the setting to the Big Picture Input tab, under "Enable Motion Controls" — it had no UI before, so the only way to reach it was hand-editing the config.

Rebased on current main.