[SourceKit] Return a default UID in getUIDForSyntaxNodeKind()
[SourceKit] Return a default UID in getUIDForSyntaxNodeKind()

Assert 0 and return a default kind, rather than calling unreachable
as a defensive fix for rdar://problem/53343735.

ahoppen/swift,atrick/swift,glessard/swift,roambotics/swift,shahmishal/swift,rudkx/swift,parkera/swift,hooman/swift,CodaFi/swift,xwu/swift,nathawes/swift,lorentey/swift,tkremenek/swift,harlanhaskins/swift,jmgc/swift,lorentey/swift,JGiola/swift,JGiola/swift,stephentyrone/swift,atrick/swift,aschwaighofer/swift,lorentey/swift,tkremenek/swift,devincoughlin/swift,aschwaighofer/swift,harlanhaskins/swift,stephentyrone/swift,tkremenek/swift,harlanhaskins/swift,aschwaighofer/swift,allevato/swift,karwa/swift,xwu/swift,sschiau/swift,sschiau/swift,devincoughlin/swift,gribozavr/swift,sschiau/swift,gribozavr/swift,apple/swift,benlangmuir/swift,rudkx/swift,jmgc/swift,roambotics/swift,parkera/swift,ahoppen/swift,apple/swift,ahoppen/swift,lorentey/swift,karwa/swift,hooman/swift,karwa/swift,tkremenek/swift,devincoughlin/swift,devincoughlin/swift,gribozavr/swift,JGiola/swift,karwa/swift,stephentyrone/swift,CodaFi/swift,nathawes/swift,jckarter/swift,JGiola/swift,aschwaighofer/swift,glessard/swift,airspeedswift/swift,CodaFi/swift,shahmishal/swift,hooman/swift,benlangmuir/swift,harlanhaskins/swift,devincoughlin/swift,devincoughlin/swift,devincoughlin/swift,stephentyrone/swift,jckarter/swift,nathawes/swift,atrick/swift,jckarter/swift,jckarter/swift,harlanhaskins/swift,benlangmuir/swift,jmgc/swift,glessard/swift,parkera/swift,lorentey/swift,aschwaighofer/swift,atrick/swift,rudkx/swift,glessard/swift,shahmishal/swift,xwu/swift,stephentyrone/swift,gregomni/swift,parkera/swift,jckarter/swift,gregomni/swift,benlangmuir/swift,airspeedswift/swift,aschwaighofer/swift,airspeedswift/swift,hooman/swift,karwa/swift,CodaFi/swift,harlanhaskins/swift,tkremenek/swift,gregomni/swift,gribozavr/swift,roambotics/swift,gribozavr/swift,CodaFi/swift,benlangmuir/swift,jckarter/swift,hooman/swift,allevato/swift,parkera/swift,ahoppen/swift,sschiau/swift,atrick/swift,tkremenek/swift,gribozavr/swift,allevato/swift,ahoppen/swift,airspeedswift/swift,nathawes/swift,sschiau/swift,rudkx/swift,airspeedswift/swift,gregomni/swift,roambotics/swift,allevato/swift,karwa/swift,glessard/swift,rudkx/swift,shahmishal/swift,lorentey/swift,xwu/swift,atrick/swift,sschiau/swift,allevato/swift,parkera/swift,hooman/swift,roambotics/swift,airspeedswift/swift,stephentyrone/swift,CodaFi/swift,roambotics/swift,apple/swift,JGiola/swift,xwu/swift,karwa/swift,jmgc/swift,benlangmuir/swift,CodaFi/swift,allevato/swift,apple/swift,sschiau/swift,devincoughlin/swift,parkera/swift,ahoppen/swift,xwu/swift,shahmishal/swift,nathawes/swift,karwa/swift,JGiola/swift,hooman/swift,jmgc/swift,lorentey/swift,stephentyrone/swift,harlanhaskins/swift,shahmishal/swift,gregomni/swift,xwu/swift,jmgc/swift,jckarter/swift,sschiau/swift,jmgc/swift,gregomni/swift,apple/swift,glessard/swift,gribozavr/swift,gribozavr/swift,shahmishal/swift,rudkx/swift,nathawes/swift,allevato/swift,parkera/swift,tkremenek/swift,shahmishal/swift,airspeedswift/swift,apple/swift,nathawes/swift,lorentey/swift,aschwaighofer/swift