Added A_SetViewPos(Vector3 Offset, int Flags = -1)

- Offset: The offset from the actor's view to move the camera about.
 - Flags: (Default is -1, which means don't change flags)
  - VPSF_ABSOLUTEOFFSET: Don't include actor angles in calculation.
  - VPSF_ABSOLUTEPOS: Position is absolute, and disables all transformations. Modders are responsible for being portal aware!

Notes:
- `ViewPos` in Actor will be `null` until A_SetViewPos is called for the first time.

**Issues:**
- Hiding sprite while in portal incomplete.

src/rendering/r_utility.h

@@ -43,7 +43,7 @@ struct FRenderViewpoint
 	
 	int				extralight;		// extralight to be added to this viewpoint
 	bool			showviewer;		// show the camera actor?
-
+	bool			NoPortalPath;	// Disable portal interpolation path for actor viewpos.
 
 	void SetViewAngle(const FViewWindow &viewwindow);