Changed handleDiagnostic to take a format string and format args instead of the formatted string

This allows diagnostic consumers to modify the way formatting of diagnostics is performed.
rdar://problem/31305854

tools/SourceKit/lib/SwiftLang/SwiftASTManager.cpp

@@ -46,7 +46,9 @@ public:
   StreamDiagConsumer(llvm::raw_ostream &OS) : OS(OS) {}
 
   void handleDiagnostic(SourceManager &SM, SourceLoc Loc,
-                        DiagnosticKind Kind, StringRef Text,
+                        DiagnosticKind Kind,
+                        StringRef FormatString,
+                        ArrayRef<DiagnosticArgument> FormatArgs,
                         const DiagnosticInfo &Info) override {
     // FIXME: Print location info if available.
     switch (Kind) {
@@ -54,7 +56,7 @@ public:
       case DiagnosticKind::Warning: OS << "warning: "; break;
       case DiagnosticKind::Note: OS << "note: "; break;
     }
-    OS << Text;
+    DiagnosticEngine::formatDiagnosticText(OS, FormatString, FormatArgs);
   }
 };
 } // end anonymous namespace