Add AirTerminalSingleDuctInletSideMixer

What this really means is that you can now attach AirLoopHVAC systems to
ZoneHVACComponents.  But... Only ZoneHVACFourPipeFanCoil is supported by
EnergyPlus right now, but the work in OS is at the base class level
ZoneHVACComponent.  Other ZoneHVACComponent derived classes are only
touched for minor house keeping (making ::inletPort ::outletPort const).

ZoneHVACComponent now derives from HVACComponent and implements
HVACComponent::addToNode, which you can use to add four pipe fan coils
to the AirTerminalSingleDuctInletSideMixer's outlet node.

[#75621100]