[SourceKit] Move all options into a common options struct

With more options coming for incremental syntax parsing, the list of
arguments will grow way to large and unhandy, so just extract them into
one common struct.

tools/SourceKit/lib/SwiftLang/SwiftLangSupport.h

@@ -397,7 +397,7 @@ public:
   void
   codeCompleteSetCustom(ArrayRef<CustomCompletionInfo> completions) override;
 
-  void editorOpen(StringRef Name, llvm::MemoryBuffer *Buf, bool EnableSyntaxMap,
+  void editorOpen(StringRef Name, llvm::MemoryBuffer *Buf,
                   EditorConsumer &Consumer,
                   ArrayRef<const char *> Args) override;