Add plugin parameter to corelocation to prevent auto-pause on iOS

This adds the parameter allowAutoPause to the corelocation backend
which modifies m_locationManager.pausesLocationUpdatesAutomatically.

This is needed to enable location sharing apps.
As the default behaviour of iOS is to pause positioning updates once
a user stays at the same spot for a longer time period.
By setting this parameter to false, positioning updates will continue.

[ChangeLog][QGeoPositionInfo][iOS] Intoroduce a plugin parameter
that allows to control the location update behavior when an
application is moved to the background. By default the updates are
stopped in such case to align with the default iOS behavior, and
also for backwards compatibility.

Change-Id: I56b96246f7022173bfbfa0a3c904e23ba9227b97
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>