Reimplement labeled statement shadowing using ASTScope.
Reimplement labeled statement shadowing using ASTScope.

Switch the "shadowing" check for labeled statements over to using the
ASTScope-based lookup of visible labeled statements.

hooman/swift,atrick/swift,rudkx/swift,apple/swift,tkremenek/swift,atrick/swift,jmgc/swift,rudkx/swift,hooman/swift,glessard/swift,ahoppen/swift,xwu/swift,airspeedswift/swift,nathawes/swift,atrick/swift,rudkx/swift,parkera/swift,rudkx/swift,ahoppen/swift,xwu/swift,hooman/swift,CodaFi/swift,xwu/swift,ahoppen/swift,gregomni/swift,nathawes/swift,nathawes/swift,airspeedswift/swift,gregomni/swift,CodaFi/swift,gregomni/swift,glessard/swift,xwu/swift,JGiola/swift,xwu/swift,tkremenek/swift,apple/swift,JGiola/swift,CodaFi/swift,xwu/swift,hooman/swift,glessard/swift,hooman/swift,xwu/swift,allevato/swift,roambotics/swift,glessard/swift,jmgc/swift,parkera/swift,benlangmuir/swift,apple/swift,roambotics/swift,airspeedswift/swift,tkremenek/swift,roambotics/swift,ahoppen/swift,apple/swift,CodaFi/swift,nathawes/swift,benlangmuir/swift,allevato/swift,tkremenek/swift,nathawes/swift,hooman/swift,roambotics/swift,jmgc/swift,allevato/swift,airspeedswift/swift,JGiola/swift,benlangmuir/swift,allevato/swift,tkremenek/swift,parkera/swift,parkera/swift,atrick/swift,atrick/swift,gregomni/swift,jmgc/swift,tkremenek/swift,gregomni/swift,roambotics/swift,nathawes/swift,benlangmuir/swift,ahoppen/swift,tkremenek/swift,allevato/swift,JGiola/swift,CodaFi/swift,rudkx/swift,parkera/swift,benlangmuir/swift,ahoppen/swift,airspeedswift/swift,parkera/swift,gregomni/swift,jmgc/swift,JGiola/swift,apple/swift,CodaFi/swift,parkera/swift,airspeedswift/swift,glessard/swift,benlangmuir/swift,jmgc/swift,JGiola/swift,nathawes/swift,allevato/swift,allevato/swift,roambotics/swift,airspeedswift/swift,hooman/swift,parkera/swift,rudkx/swift,apple/swift,jmgc/swift,CodaFi/swift,atrick/swift,glessard/swift