Cancel download prompt

[mavduevskiy]

Relates to the ...fenix/18160.
Short version:
adding a prompt that warns the user about cancellation of active downloads.

Long version:
We are adding new business logic to closing private tabs. Now it will check for active private downloads.

After a lot of consideration if it should be implemented as part of the feature/storage inside AC or inside the controller/interactor inside Fenix, we agreed that AC implementation would be much more verbose. Hence, AC recieves the prompt itself, but the calling logic would reside in the Fenix project.

Logic:
If the action leads to having zero private tabs, app warns the user that all private downloads will be finished.
A user can

1. close each private tab individually,
2. close all private tabs from the three dot menu and
3. close all private tabs from Firefox Private notification with the corresponding action.

Current implementation of the warning on the fenix side would cover the first two scenarios.

┆Issue is synchronized with this Jira Task