Add markdown viewer plugin

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

src/plugins/markdownviewer/markdowndocument.cpp

@@ -0,0 +1,18 @@
+// Copyright (C) 2023 Tasuku Suzuki
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+#include "markdowndocument.h"
+#include "markdownviewerconstants.h"
+
+namespace Markdown {
+namespace Internal {
+
+MarkdownDocument::MarkdownDocument()
+{
+    setId(Constants::MARKDOWNVIEWER_ID);
+    setMimeType(QLatin1String(Constants::MARKDOWNVIEWER_MIME_TYPE));
+    connect(this, &MarkdownDocument::mimeTypeChanged, this, &MarkdownDocument::changed);
+}
+
+} // namespace Internal
+} // namespace Markdown