TextEditor example: open file as text

The texteditor is made to open text, and in this case it makes sense to
pass the Text flag to the QFile::open call in the example code.

Pick-to: 6.5
Task-number: QTBUG-118636
Change-Id: I936610945aa6e2f67b29ce6f5c559a2b942fc718
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
Reviewed-by: Olivier De Cannière <olivier.decanniere@qt.io>
(cherry picked from commit 743065d7fe)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

examples/quickcontrols/texteditor/documenthandler.cpp

@@ -154,7 +154,7 @@ void DocumentHandler::load(const QUrl &fileUrl)
     if (QFile::exists(fileName)) {
         QMimeType mime = QMimeDatabase().mimeTypeForFile(fileName);
         QFile file(fileName);
-        if (file.open(QFile::ReadOnly)) {
+        if (file.open(QFile::ReadOnly | QFile::Text)) {
             QByteArray data = file.readAll();
             if (QTextDocument *doc = textDocument()) {
                 doc->setBaseUrl(path.adjusted(QUrl::RemoveFilename));