cmd/trace: annotation proc start/stop with thread and proc always

cmd/trace: annotation proc start/stop with thread and proc always

In the proc view, the thread ID is useful. In the thread view, the proc
ID is useful. Add both in both cases forever more.

Change-Id: I9cb7bd67a21ee17d865c25d73b2049b3da7aefbc
Reviewed-on: https://go-review.googlesource.com/c/go/+/720402
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>