add test case for unicodeScalars

Author: karimhamdanali

swift/ql/test/library-tests/dataflow/taint/string.swift

@@ -114,13 +114,16 @@ func taintThroughData() {
 
 func sink(arg: String.UTF8View) {}
 func sink(arg: ContiguousArray<CChar>) {}
+func sink(arg: String.UnicodeScalarView) {}
 
 func taintThroughStringFields() {
   let clean = ""
   let tainted = source2().utf8
   let taintedCString = source2().utf8CString
+  let taintedUnicodeScalars = source2().unicodeScalars
 
   sink(arg: clean)
-  sink(arg: tainted) // $ tainted=120
-  sink(arg: taintedCString) // $ tainted=121
+  sink(arg: tainted) // $ tainted=121
+  sink(arg: taintedCString) // $ tainted=122
+  sink(arg: taintedUnicodeScalars) // $ tainted=123
 }