swift234

SIL: Lower closure capture params out-of-band from the formal type.

Instead of bodging a representation of the SIL capture parameters for a closure into the formal type of closure SILDeclRefs, introduce those parameters in a separate lowering step. This lets us clean up some TypeLowering code that was tolerating things like SILBoxTypes and naked LValueTypes in formal types for nefarious ends (though requires some hacks in SILGen to keep the representation of curry levels consistent, which is something I hope to clean up next). This also decouples the handling of captures from the handling of other parameters, which should enable us to make them +0. For now, there should be NFC.