The `ErrorOutput` field is not used in the compiler protocol because the
compiler never writes to stderr. This was complicating the code path for
no good reason and hence I decided to remove it.

Refactor a bit and clean up some comments to help make the flow of data
a bit clearer here.

This change adds structured messages to the binlog about the behavior of
the compiler server. These messages will help users, our own developers
and automation understand the behavior of the compiler server within a
build.

Co-authored-by: Sam Harwell <[email protected]>

Co-authored-by: Rikki Gibson <[email protected]>