This implements getting the information needed to show the date of a backup in the restore component and showing the password input if that backup is encrypted.
- Adds a `getBackupFileInfo` method to `BackupService` that will call `sampleArchive` for a passed backup file and update the `backupFileInfo` in the state with a subset of that info.
- Update the `GetBackupFileInfo` event handler in `BackupUIParent` to use the new `getBackupFileInfo` method.
Differential Revision: https://phabricator.services.mozilla.com/D214899
fe16fc1d18