Report progress from high-level functions that use map()

[jennybc]

Report progress when we use purrr::map() to make one API call per file. For example, drive_reveal() can be very slow and it would be good to know what it's doing.

[jbayham]

On a related note, it would also be nice to have a progress bar for large downloads using drive_download()

[jennybc]

This will be handled through some combination of adopting httr2 and using batch requests #360. I'm certainly not going to do any more work on the sub-optimal purrr stuff. The next step is to remove it.