[lldb] Don't report all progress event as completed. (#84281)

Currently, progress events reported by the ProgressManager and broadcast
to eBroadcastBitProgressCategory always specify they're complete. The
problem is that the ProgressManager reports kNonDeterministicTotal for
both the total and the completed number of (sub)events. Because the
values are the same, the event reports itself as complete.

This patch fixes the issue by reporting 0 as the completed value for the
start event and kNonDeterministicTotal for the end event.