iOS: Feed the gyroscope into tilt input

Same as Android: rotation rates go to NativeGyroscope, and SYSPROP_HAS_GYRO shows the "Use gyroscope" option.

Accelerometer data is now scaled from g to m/s^2, like Android's. Tilt normalizes it, but the gyro fusion only trusts the accelerometer when it reads about 9.81, so in g it would never correct drift.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Common/System/NativeApp.h

@@ -66,6 +66,7 @@ void NativeResized();
 void NativeTouch(const TouchInput &touch);
 bool NativeKey(const KeyInput &key);
 void NativeAxis(const AxisInput *axis, size_t count);
+// In m/s^2, the way Android reports it: about +9.81 on z with the device lying screen up.
 void NativeAccelerometer(float tiltX, float tiltY, float tiltZ);
 // Angular rates in rad/s around the NativeAccelerometer axes. The timestamp is in seconds, on any clock (only deltas are used).
 void NativeGyroscope(float x, float y, float z, double timestamp);