[TIMOB-18480] Update doc coverage to look at diff between TitaniumKit and TitaniumWindows proxies

Currently, it appears that the doc coverage scripts for Windows use TitaniumKit t determine what modules/classes/methods are implemented. The issue is that for _some_ of the APIs we will implement them there, but for most we will implement the method/setter down in the base classes in TitaniumWindows. So there's actually two levels of "implementation": Whether we've defined the property/method as existing in the TitaniumKit proxy, and whether we've actually implemented it in the Windows implementation. Generally speaking, looking at the Windows implementation for setters is more accurate, but in some cases we may actually have a cross-platform impl up in TitaniumKit. It may be difficult to determine when that is the case (a good first pass my be to look and see if the method is declared final in TK, which means we don't expect subclasses to have to override/implement something).