[RF] Reduce the number of global statics in RooFit

Factories in RooFit are often handled using global static pointers
that are initialised and deleted manually.
Making these function-local statics makes this process automatic.

- This was done for NumGen(Config|Factory), NumInt(Config|Factory),
RooMsgService, RooNameReg, ExpensiveObjectCache, RooRealConstant,
RooResolutionModel
- It further required breaking a cyclical dependency when constructing RooNumIntFactory.
- Finally also fix doxygen for RooResolutionModel