Redefine the set of bootstrap phases to allow display of finer-grained
progress in the early connection stages of connecting to a relay.
This includes adding intermediate phases for proxy and PT connections.
Also add a separate new phase to indicate obtaining enough directory
info to build circuits so we can report that independently of actually
initiating an ORCONN to build the first application circuit.
Previously, we would claim to be connecting to a relay when we had
merely finished obtaining directory info.
Part of ticket 27167.
Replace a few invocations of control_event_bootstrap() with calls from
the bootstrap tracker subsystem. This mostly leaves behavior
unchanged. The actual behavior changes come in the next commit.
Part of ticket 27167.
