View Angles (Part 1 - Redux) (#1002)

* Added ViewAngle/Pitch/Roll properties to actors.

- These are offsets for camera angles that allow turning the camera without affecting aim or movement direction.
- Added A_SetView<Angle/Pitch/Roll>, which will set the view direction.
- Added ABSVIEWANGLES flag, used to make the view absolute instead of an offset.

* Converted functions to be direct-native.

src/scripting/thingdef_data.cpp

@@ -325,6 +325,7 @@ static FFlagDef ActorFlagDefs[]=
 	DEFINE_FLAG(MF8, NOFRICTIONBOUNCE, AActor, flags8),
 	DEFINE_FLAG(MF8, RETARGETAFTERSLAM, AActor, flags8),
 	DEFINE_FLAG(MF8, STOPRAILS, AActor, flags8),
+	DEFINE_FLAG(MF8, ABSVIEWANGLES, AActor, flags8),
 
 	// Effect flags
 	DEFINE_FLAG(FX, VISIBILITYPULSE, AActor, effects),