[Reflection] Fix ReflectionContext::allocationMetadataPointer.
[Reflection] Fix ReflectionContext::allocationMetadataPointer.

The definition of GenericMetadataCacheEntry was wrong, causing the function to return garbage.

apple/swift,atrick/swift,benlangmuir/swift,glessard/swift,roambotics/swift,glessard/swift,rudkx/swift,glessard/swift,rudkx/swift,atrick/swift,ahoppen/swift,JGiola/swift,ahoppen/swift,apple/swift,atrick/swift,JGiola/swift,apple/swift,JGiola/swift,benlangmuir/swift,gregomni/swift,JGiola/swift,gregomni/swift,gregomni/swift,apple/swift,benlangmuir/swift,gregomni/swift,JGiola/swift,roambotics/swift,gregomni/swift,apple/swift,rudkx/swift,ahoppen/swift,ahoppen/swift,atrick/swift,roambotics/swift,roambotics/swift,glessard/swift,ahoppen/swift,benlangmuir/swift,ahoppen/swift,glessard/swift,gregomni/swift,JGiola/swift,roambotics/swift,benlangmuir/swift,rudkx/swift,glessard/swift,atrick/swift,atrick/swift,roambotics/swift,benlangmuir/swift,rudkx/swift,rudkx/swift,apple/swift