cmd/trace/v2: emit regions in the goroutine-oriented task view
This change emits regions in the goroutine-oriented task view (the
/trace endpoint with the taskid query variable set) in the same way the
old cmd/trace does.
For #60773.
Fixes #63960.
Change-Id: If6c3e7072c694c84a7d2d6c34df668f48d3acc2a
Reviewed-on: https://go-review.googlesource.com/c/go/+/543995 Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>