tests: make qprefdisplay test file

Remove display tests from testpreferences and make a new file

Signed-off-by: Jan Iversen <jani@apache.org>

tests/testqPrefDisplay.h

@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef TESTQPREFDISPLAY_H
+#define TESTQPREFDISPLAY_H
+
+#include <QTest>
+#include <functional>
+
+class TestQPrefDisplay : public QObject
+{
+	Q_OBJECT
+private slots:
+	void initTestCase();
+	void test1();
+};
+
+#endif // TESTQPREFDISPLAY_H