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/qmljstools/qmljscodestylesettingspage.cpp

@@ -113,8 +113,7 @@ void QmlJSCodeStylePreferencesWidget::updatePreview()
     QTextCursor tc = m_ui->previewTextEdit->textCursor();
     tc.beginEditBlock();
     while (block.isValid()) {
-        m_ui->previewTextEdit->textDocument()->indenter()
-                ->indentBlock(doc, block, QChar::Null, ts);
+        m_ui->previewTextEdit->textDocument()->indenter()->indentBlock(block, QChar::Null, ts);
         block = block.next();
     }
     tc.endEditBlock();