Performance enhancement for `cargo clean`

[weihanglo]

Problem

Spinned out from #10236 (comment)

#10236 introduces a progress bar for cargo clean, which has a slight performance hit (0-10%). There are still some possibilities we can explore in this area to enhance its performance.

Proposed Solution

Some directions (and they might be entangled with each other)

• Parallelize the file removing process.
• The progress bar ticks too often, and might hurt the performance over a slow network connection.
• Fall back to non progress bar clean behavior when with --quiet flag on.

Notes

Unless this affects people a lot, I feel like it is not a high-priority task. Anyone interested in it should discuss with the cargo team first, though due to the limited review bandwidth, the team might not respond instantly.

[ilyapopov]

For historical precedent: in 2016 npm had an issue where progress bar was slowing down npm install in some cases by a factor of 2.

npm/npm#11283