Add camera capabilities + metadata to QGeoMapType/QDeclarativeGeoMapType

This patch enriches QGeoMapType/QDeclarativeGeoMapType embedding into
this object the camera capabilities for this type, that are then exposed
via a new QML Type, CameraCapabilities, and custom metadata in form
of a QVariantMap, that can be accessed via the new metadata property.

[ChangeLog][QtLocation][QDeclarativeGeoMapType] Added CameraCapabilities
and metadata properties to QDeclarativeGeoMapType.

Task-number: QTBUG-58931
Change-Id: I97a8852fbb3bbac88fdbf0d47e8247ea7ed1f31e
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>