Use ScriptInterface::CreateObject for ToJSVal<CColor>, and for ToJSVal<Grid<u8> >, ToJSVal<Grid<u16> > used by the AIManager obtaining the pathfinder grid.

Make that function static, so that it can be used for these functions without slowly having to obtain the ScriptInterface instance using GetScriptInterfaceAndCBData just to get the JSContext again.
Remove few redundant conversions for CreateObject arguments.

Differential Revision: https://code.wildfiregames.com/D2128
Tested on: gcc 9.1.0, clang 8.0.1, Jenkins
Tedious performance testing in: D2128, D2127