Implement/match Act3::Notify (#1200)

* Implement/match Act3::Notify

* Fix typo

LEGO1/lego/legoomni/include/helicopter.h

@@ -5,6 +5,8 @@
 #include "legostate.h"
 #include "realtime/matrix.h"
 
+class Act3;
+
 // VTABLE: LEGO1 0x100d5418
 // SIZE 0x0c
 class HelicopterState : public LegoState {
@@ -78,6 +80,9 @@ public:
 	// SYNTHETIC: LEGO1 0x10003210
 	// Helicopter::`scalar deleting destructor'
 
+	// m_state is accessed directly from Act3; confirmed by BETA10
+	friend class Act3;
+
 protected:
 	MxMatrix m_unk0x160;              // 0x160
 	MxMatrix m_unk0x1a8;              // 0x1a8