[stdlib] location/formLocation => index/formIndex

stdlib/public/core/UnicodeScalar.swift

@@ -248,7 +248,7 @@ extension UnicodeScalar.UTF16View : Collection {
   ///
   /// `endIndex` is not a valid argument to `subscript`, and is always
   /// reachable from `startIndex` by zero or more applications of
-  /// `location(after:)`.
+  /// `index(after:)`.
   var endIndex: Int {
     return 0 + UTF16.width(value)
   }