Add an unxip progress bar

[dented42]

Tell us how we can improve Xcodes
The operating system's builtin Archive Utility displays a progress bar when unxipping Xcode. It would be really helpful to have something similar in Xcodes.

Is your feature request related to a problem? Please describe.
Unxipping takes a really long time, a progress bar would help users determine if the unxipping has frozen completely or is progressing extremely slowly. This would have been helpful when the unxipping step took several days before I gave up and retried.

What would you like to see? How would you like it to work?
A progress bar, similar to the download step. An 'approximate time remaining' would also be nice, but the perils of providing such an estimate are well known and probably not worth it.