Texteditor: Add ability to get margin from indenter

And implement it in the clang-format plugin to use the ColumnLimit from
the style. This would be quite useful if you're working on different
projects with a different ColumnLimit. This way you get an visual
representation and do not only have to rely on clang-format.

Change-Id: Ib0258e3fba6f45f0f46ce612f806527a47868ad9
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/texteditor/texteditor.h

@@ -621,6 +621,8 @@ private:
     friend class Internal::TextEditorWidgetPrivate;
     friend class Internal::TextEditorOverlay;
     friend class RefactorOverlay;
+
+    void updateVisualWrapColumn();
 };
 
 class TEXTEDITOR_EXPORT TextEditorLinkLabel : public Utils::ElidingLabel