Unpack progress

[djc]

cc @FranciscoTGouveia

unpack-progress.mov

[FranciscoTGouveia]

After testing the changes, it seems that the ticking speed for the unpacking phase is so high that it feels a bit disconcerting.
Would it be possible to slow it down?

Moreover, I would like to ask whether this change is a step toward achieving concurrent downloads & installs (without spawning an additional thread).
If so, I believe the issue where progress bars stop updating during installation (as discussed in #4570) remains, and I do not think that this will help in facilitating that -- I might be overlooking something here.
Even though downloads continue in the background, the blocking install call never yields, so the progress bars never get the chance to update during installation.

I think that making install async is ultimately the only way to avoid the spawning of an additional thread.

[rami3l]

@FranciscoTGouveia In the current stable version we actually have progress reporting for unpacking as well, however it's behind a 1-second timeout so no one actually sees it except for the docs component.

Thus, I think your concern is reasonable, and even though it's probably great for @djc to restore that behavior here, it might be worth it to make it closer to the original in terms of lowering the number of ticks indeed.

[rami3l]

Just tested locally. The code looks okay but I share @FranciscoTGouveia's concern: it looks like the tick frequency is way too high...

[djc]

Changed it to display a progress bar while unpacking. See the movie in the PR description (which also includes #4602).