Fix crash tst_qqmllanguage

qmlClearTypeRegistrations() shouldn't be called when instances of
QQmlEngine are still open. This can lead to unexpected behavior.

For the qmlClearTypeRegistrations() function there is separate
autotest

Task-number: QTBUG-32078
Change-Id: I32612bc82602593d902bbffc58911e427b50524f
Reviewed-by: Alan Alpert <aalpert@blackberry.com>
Fix qmlClearEnginePlugins() to clear engine plugins.

Task-number: QTBUG-32078

Change-Id: I2d3aeb6b91ffdb9b8c70ad93d1e43daada84fb7f
Reviewed-by: Alan Alpert (Personal) <416365416c@gmail.com>
Removed the static intialized boolean of qquickitemsmodule.

This prevents a reregistration of the all QQuick2 types when
qmlClearTypeRegistrations() is called

Task-number: QTBUG-32078
Change-Id: I33b4c069183d6344a2f14b4147eaa7056c3b72b9
Reviewed-by: Alan Alpert <aalpert@blackberry.com>