ClangFormat: Refactor indenter to allow ClangFormat unit-tests

We do not build texteditor files in unit-tests so some tricks
were required to make ClangFormatIndenter available.

First simple unit-test proofs it builds and runs.

Change-Id: I81d5ea099bd27fd1c1ed8b5b7877299dcc62a67f
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/clangformat/clangformatplugin.cpp

@@ -84,9 +84,9 @@ public:
         return nullptr;
     }
 
-    TextEditor::Indenter *createIndenter() const override
+    TextEditor::Indenter *createIndenter(QTextDocument *doc) const override
     {
-        return new ClangFormatIndenter();
+        return new ClangFormatIndenter(doc);
     }
 };