cmd/trace/v2: add support for the goroutine-oriented task view
This change adds support for a goroutine-oriented task view via the
/trace?taskid=<taskid> endpoint. This works but it's missing regions.
That will be implemented in a follow-up CL.
For #60773.
For #63960.
Change-Id: I086694143e5c71596ac22fc551416868f0b80923
Reviewed-on: https://go-review.googlesource.com/c/go/+/543937
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com> Reviewed-by: Michael Pratt <mpratt@google.com>