Split off Object-related functions from ScriptInterface

Follows 34b1920e7b.

This splits off the object-related functions, such as
[Set/Get/Has]Property, CreateObject, CreateArray, FreezeObject.

It also puts the definitions in the header itself, which might end up
with faster code here & there, though perhaps slower compilation time
(somewhat doubtful since we already included most things anyways).

Differential Revision: https://code.wildfiregames.com/D3956
This was SVN commit r25430.

source/graphics/scripting/JSInterface_GameView.cpp

@@ -1,4 +1,4 @@
-/* Copyright (C) 2020 Wildfire Games.
+/* Copyright (C) 2021 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -80,7 +80,7 @@ JS::Value GetCameraPivot(const ScriptRequest& rq)
 		pivot = g_Game->GetView()->GetCameraPivot();
 
 	JS::RootedValue pivotValue(rq.cx);
-	ScriptInterface::CreateObject(rq, &pivotValue, "x", pivot.X, "z", pivot.Z);
+	Script::CreateObject(rq, &pivotValue, "x", pivot.X, "z", pivot.Z);
 	return pivotValue;
 }