We have to ensure to properly call all Component complete handlers.
A single component usually has QQmlComponentAttached objects,
which we have to iterate over.
Therefore emitComponentCompleteSignalForAttachedProperty() is not correct.
Task-number: QDS-269
Change-Id: I4aed5d511f9f6e21f72efb955fc6db21b70e7c42
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>