Android: Detect the accelerometer and gyro instead of assuming them

SYSPROP_HAS_ACCELEROMETER was true for every phone and tablet, whether or
not it had the sensor. The activity now tells the native side what the
sensor manager found, which also answers the new SYSPROP_HAS_GYRO. VR
headsets still report neither. Every other platform returns false for the
gyro for now.

The "Use gyroscope" checkbox uses the new property instead of waiting for
gyro data to show up.

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

Core/TiltEventProcessor.cpp

@@ -371,10 +371,6 @@ bool GyroActive() {
 	return g_seenGyro && time_now_d() - g_lastGyroArrival < 0.2;
 }
 
-bool HasSeenGyro() {
-	return g_seenGyro;
-}
-
 void ResetTiltEvents() {
 	// Reset the buttons we have marked pressed.
 	__CtrlUpdateButtons(0, tiltButtonsDown);