Instead of coding some arguments to extraId(state) we provide now a
std::variant there extra arguments can be saved. Because it's a
std::variant it can be easlily extended by new structs. There is a new
synchronous interface too. It has an extra method for QIcon which saves
icons in an extra table. It would be even nicer if we would have a
mipmap image too. So we could do it asynchonously too but so far it works
only in the main thread.
Task-number: QDS-3579
Fixes: QDS-3584
Change-Id: If368d84d82308a91a5f4f037021e749c9ef868ed
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>
