[SE-0304] Add `UnsafeCurrentTask.cancel()`.
[SE-0304] Add `UnsafeCurrentTask.cancel()`.

parkera/swift,roambotics/swift,rudkx/swift,gregomni/swift,hooman/swift,hooman/swift,parkera/swift,glessard/swift,glessard/swift,glessard/swift,hooman/swift,JGiola/swift,ahoppen/swift,apple/swift,roambotics/swift,xwu/swift,xwu/swift,tkremenek/swift,roambotics/swift,apple/swift,ahoppen/swift,hooman/swift,gregomni/swift,tkremenek/swift,atrick/swift,roambotics/swift,parkera/swift,rudkx/swift,xwu/swift,apple/swift,gregomni/swift,JGiola/swift,apple/swift,hooman/swift,xwu/swift,atrick/swift,hooman/swift,benlangmuir/swift,ahoppen/swift,parkera/swift,atrick/swift,glessard/swift,gregomni/swift,JGiola/swift,xwu/swift,benlangmuir/swift,xwu/swift,tkremenek/swift,JGiola/swift,atrick/swift,atrick/swift,ahoppen/swift,xwu/swift,roambotics/swift,rudkx/swift,tkremenek/swift,tkremenek/swift,benlangmuir/swift,benlangmuir/swift,atrick/swift,hooman/swift,benlangmuir/swift,apple/swift,gregomni/swift,benlangmuir/swift,ahoppen/swift,rudkx/swift,gregomni/swift,glessard/swift,glessard/swift,parkera/swift,parkera/swift,tkremenek/swift,JGiola/swift,roambotics/swift,rudkx/swift,parkera/swift,JGiola/swift,apple/swift,tkremenek/swift,parkera/swift,ahoppen/swift,rudkx/swift