Add markdown viewer plugin

Fixes: QTCREATORBUG-27883
Change-Id: Ie4099b8a322797d300bc15a80333bcb361ecafc3
Reviewed-by: André Hartmann <aha_1980@gmx.de>

src/plugins/markdownviewer/markdownviewerwidget.h

@@ -0,0 +1,37 @@
+// Copyright (C) 2023 Tasuku Suzuki
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+#pragma once
+
+#include <coreplugin/minisplitter.h>
+#include <utils/fileutils.h>
+
+namespace Core { class IDocument; }
+
+namespace Markdown {
+namespace Internal {
+
+class MarkdownViewerWidget : public Core::MiniSplitter
+{
+    Q_OBJECT
+    Q_PROPERTY(bool editorVisible READ isEditorVisible WRITE setEditorVisible NOTIFY editorVisibleChanged)
+public:
+    explicit MarkdownViewerWidget();
+    ~MarkdownViewerWidget() override;
+
+    Core::IDocument *document() const;
+
+    bool isEditorVisible() const;
+
+public slots:
+    void setEditorVisible(bool editorVisible);
+
+signals:
+    void editorVisibleChanged(bool editorVisible);
+
+private:
+    struct MarkdownViewerWidgetPrivate *d;
+};
+
+} // namespace Internal
+} // namespace Markdown