[CostModel][X86] getCastInstrCost - update cost tables to support CostKinds

Add TypeConversionCostKindTblEntry to hold the costs kinds and update the cast tables to take the existing default codesize/latency/sizelatency values (I'll update these values in future commits).

I've moved AdjustCost to the end of the function to ensure we don't accidentally use it, apart from when we fallback to default cost calculations.