ekf2-fake pos: add valid fake position fusion

This is similar to fake pos but is only used when the ekf has an
external information telling it that the vehicle is not changing
position. This information can then be used to keep a valid local
position even when the vehicle isn't exactly at rest.

src/modules/ekf2/EKF/ekf.h

@@ -1132,7 +1132,7 @@ private:
 	}
 
 	void resetFakePosFusion();
-	void stopFakePosFusion();
+	bool runFakePosStateMachine(bool enable_condition_passing, bool status_flag, estimator_aid_source2d_s &aid_src);
 
 	// reset the quaternion states and covariances to the new yaw value, preserving the roll and pitch
 	// yaw : Euler yaw angle (rad)