Enhance support for the content in Progress events

[plaird]

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Progress events are the sketchy part of town for BEP. They contain unstructured output from the underlying rule executions, have weird formatting symbols (ncurses?), and contain the raw progress bar data:

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The existing progress event does the scraping of the weird characters, but there is a lot more that can be done to allow an event consumer to piece together the chain of progress events. Use the progress bar data for something useful? Implement custom parsers for different build tools (like javac) to make better sense of the data?