Searching `in:archive` sorts by archival date.

[Medium article about recovering archived emails](https://medium.com/@MattGyverLee/oops-i-just-archived-a-bunch-of-gmail-messages-71aae70322d7):

> To search for recently archived emails in Gmail, open Gmail and in the
> search box, type “in:archive” (without the quotes) and press enter. It
> will show only messages that have been archived (not including
> messages in the inbox like All Mail).
>
> The magic of this command is that now the dates of the messages
> represent the date of archival (not the date of receipt)! The results
> should already be sorted by date that the message was archived.