internal/trace: implement goroutine analysis for v2 traces

For #63960.

Change-Id: I1efe35435e32623aba894a915114e394570ebc56
Reviewed-on: https://go-review.googlesource.com/c/go/+/540259
Reviewed-by: Michael Pratt <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: mknyszek