A previous commit Q_CORE_EXPORTed this class so it could be used in
tst_qevent. But we can also keep it Q_AUTOTEST_EXPORTed and make the
testing of the class subject to QT_BUILD_INTERNAL on the test side.
That's what this patch does.
Change-Id: I9bd5f80ada856b7db4b39dfb59b32bd825416c13
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>