TextEditor: get CompletionAssistProvider from editor.

And not from the global object pool. This way, the editors that have
different highlighters for various language dialects, or editors that
support multiple languages in a single editor, can decide themselves on
what CompletionAssistProvider to provide.

Change-Id: Ieebc4a8e7b3de6470fdb8103035aa3b8b2ba6598
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>

src/plugins/qmljseditor/qmljseditoreditable.h

@@ -51,6 +51,8 @@ public:
     bool isDesignModePreferred() const;
 
     const Utils::CommentDefinition *commentDefinition() const;
+
+    TextEditor::CompletionAssistProvider *completionAssistProvider();
 private:
     Utils::CommentDefinition m_commentDefinition;
 };