[MCSchedModel] Variant class support in computeInstrLatency and getReciprocalThroughput

[RKSimon]

Bugzilla Link	38030
Version	trunk
OS	Windows NT
Blocks	#35898
CC	@adibiagio,@atrick,@legrosbuffle,@gchatelet,@hfinkel

Extended Description

Both MCSchedModel::computeInstrLatency and MCSchedModel::getReciprocalThroughput are missing support for variant classes from some versions of the methods.

They either assert if MCSchedClassDesc.isVariant() or don't take it into account at all (and give some very odd latency/throughput numbers...). This appears to be at least in part to them not always having access to a MCInst instance which prevents them resolving with resolveVariantSchedClass.

Some of these methods may be not in use and can be removed, while for others we need some way to resolve the variant to a default (worst case?) sched class.