cmd/go: add trace events for each action

This change adds a trace event for each action and also
annotates each of the action execution goroutines with trace.Goroutine
so that the actions eaxecuted by each goroutine appear on different threads in
the chrome trace viewer.

Updates #38714

Change-Id: I2e58dc5606b2e3f7f87076a61e1cc6a2014255c5
Reviewed-on: https://go-review.googlesource.com/c/go/+/248320


Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>