Verify that nil can cast to AnyHashable (#34434)
Verify that nil can cast to AnyHashable (#34434)

Optional conditionally conforms to Hashable, so for
example `Optional<Int>` must cast to AnyHashable
_even if it contains `nil`_.  This was broken up
through Swift 5.3 and was fixed by the new dynamic
cast runtime.

Add a test to ensure this stays fixed.
benlangmuir/swift,benlangmuir/swift,JGiola/swift,tkremenek/swift,tkremenek/swift,hooman/swift,jmgc/swift,atrick/swift,parkera/swift,ahoppen/swift,xwu/swift,xwu/swift,glessard/swift,apple/swift,tkremenek/swift,glessard/swift,apple/swift,tkremenek/swift,ahoppen/swift,hooman/swift,ahoppen/swift,tkremenek/swift,benlangmuir/swift,apple/swift,xwu/swift,rudkx/swift,ahoppen/swift,parkera/swift,roambotics/swift,parkera/swift,xwu/swift,rudkx/swift,atrick/swift,parkera/swift,atrick/swift,parkera/swift,JGiola/swift,apple/swift,ahoppen/swift,hooman/swift,jmgc/swift,apple/swift,hooman/swift,parkera/swift,jmgc/swift,rudkx/swift,gregomni/swift,roambotics/swift,roambotics/swift,gregomni/swift,JGiola/swift,xwu/swift,hooman/swift,jmgc/swift,jmgc/swift,parkera/swift,glessard/swift,atrick/swift,jmgc/swift,xwu/swift,roambotics/swift,xwu/swift,gregomni/swift,atrick/swift,rudkx/swift,glessard/swift,benlangmuir/swift,hooman/swift,ahoppen/swift,tkremenek/swift,roambotics/swift,rudkx/swift,gregomni/swift,gregomni/swift,gregomni/swift,glessard/swift,benlangmuir/swift,JGiola/swift,hooman/swift,parkera/swift,rudkx/swift,jmgc/swift,JGiola/swift,apple/swift,benlangmuir/swift,tkremenek/swift,atrick/swift,glessard/swift,roambotics/swift,JGiola/swift