QmlJSEditor: Move semantic highlighting to document

This ensures that we are only highlighting once, and actually do
highlight (the previous code was trying to prevent multiple rehighlights
though doing the highlighting in the editor(s), resulting in situations
where it wouldn't rehighlight at all)

Change-Id: I18f3e72e31d8076b6d1575f1a17a3f4a101163d9
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>

src/plugins/qmljseditor/qmljseditor.h

@@ -71,8 +71,6 @@ class FindReferences;
 namespace Internal {
 class QmlJSEditorDocument;
 class QmlOutlineModel;
-class SemanticHighlighter;
-
 } // namespace Internal
 
 struct QMLJSEDITOR_EXPORT Declaration
@@ -183,7 +181,6 @@ private:
     int m_oldCursorPosition;
 
     FindReferences *m_findReferences;
-    Internal::SemanticHighlighter *m_semanticHighlighter;
 };
 
 } // namespace QmlJSEditor