[TableGen][SchedModel] Introduce a new SchedPredicate that checks against SubtargetFeature (#161888)

Introduce a new SchedPredicate, `FeatureSchedPredicate`, that holds true
when a certain SubtargetFeature is enabled. This could be useful when we
want to configure a scheduling model with subtarget features.

I add this as a separate SchedPredicate rather than piggy-back on the
existing `SchedPredicate<[{....}]>` because first and foremost,
`SchedPredicate` is expected to only operate on MachineInstr, so it does
_not_ appear in `MCGenSubtargetInfo::resolveVariantSchedClass` but only
show up in `TargetGenSubtargetInfo::resolveSchedClass`. Yet I think
`FeatureSchedPredicate` will be useful for both MCInst and MachineInstr.
There is another subtle difference between `resolveVariantSchedClass`
and `resolveSchedClass` regarding how we access the MCSubtargetInfo
instance, if we really want to express `FeatureSchedPredicate` using
`SchedPredicate<[{.....}]>`.

So I thought it'll be easier to add another new SchedPredicate for
SubtargetFeature.

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