This starts to flesh out more complete overload resolution rules. A lot
of this is extremely similar to C++ however we have some key
differences. Those differences include:

* HLSL supports overload resolution in 5 contexts, whereas C++ supports
  it in 7 (DXC actually only supports 2 of those contexts).
* HLSL has two additional conversion sequence ranks.
* HLSL has more rules to disambiguate some conversions.