[Tracker] Provide better diagnostics for APFS corruption

[marcan]

If your issue got duped here: You have latent disk corruption. Follow these instructions to run First Aid and try to fix your filesystem. If that doesn't work, unfortunately, you'll have to reformat and reinstall macOS. This is an Apple bug and not caused by the installer; the installer just finds the corruption that was already there.

We should have the installer parse the diskutil output and provide a better diagnostic. This needs some thinking as to how to best do this while still providing real-time resize progress output.