Move git specific stuff out of diff editor plugin

Move it to the git plugin.

Change-Id: I8151573ed50df70776f7ebf0475dd41fb84fae83
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/diffeditor/descriptionwidgetwatcher.h

@@ -0,0 +1,60 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include "diffeditor_global.h"
+
+#include <QObject>
+
+namespace Core {
+class IDocument;
+class IEditor;
+}
+namespace TextEditor { class TextEditorWidget; }
+
+namespace DiffEditor {
+
+class DiffEditorController;
+
+class DIFFEDITOR_EXPORT DescriptionWidgetWatcher : public QObject
+{
+    Q_OBJECT
+public:
+    explicit DescriptionWidgetWatcher(DiffEditorController *controller);
+    QList<TextEditor::TextEditorWidget *> descriptionWidgets() const;
+
+signals:
+    void descriptionWidgetAdded(TextEditor::TextEditorWidget *editor);
+    void descriptionWidgetRemoved(TextEditor::TextEditorWidget *editor);
+
+private:
+    TextEditor::TextEditorWidget *descriptionWidget(Core::IEditor *editor) const;
+
+    QList<TextEditor::TextEditorWidget *> m_widgets;
+    Core::IDocument *m_document = nullptr;
+};
+
+} // namespace DiffEditor