[new compiler] Add support for implicitly defined components

[new compiler] Add support for implicitly defined components

Use-cases like

    itemDelegate: Item { ... }

implicitly define a component without the item-surrounding Component {}, base
on the fact that the property itself is of type QQmlComponent (or derived).

This means we have to synthesize a Component {} object and insert it into
the data structure.

Change-Id: I8992451a5a6732c7fd898eaf83c276dc6a8b7d19
Reviewed-by: Lars Knoll <lars.knoll@digia.com>