texteditor: Add Select Next Match function

Adds an Action to select the next occurrence(s) of the currently selected text.

Change-Id: I37e23a3c2d1651ec4898fac53d75044d92ed7079
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/texteditor/texteditor.h

@@ -384,6 +384,7 @@ public:
     void updateTextCodecLabel();
     void selectLineEnding(int index);
     void updateTextLineEndingLabel();
+    void addSelectionNextFindMatch();
 
     void gotoBlockStart();
     void gotoBlockEnd();