Avoid roundtrips in QML debugger protocol.

Currently, we get output like

{"name":"maxIndex","ref":24}

To save roundtrips it would be beneficial to have also value, type, and "expandability" included,

{"name":"maxIndex","ref":24,"value":130,"type":"number","hasChildren":false}

(the hasChildren would only be needed for items that potentially have children, for numbers, no children could remain implicit.