Split off Object-related functions from ScriptInterface
Follows rP25366.
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