[test] add tests of String-from-C-string String overloads
[test] add tests of String-from-C-string String overloads

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