runtime: update gctrace docs and print lastStackScan instead of max
This change updates the gctrace docs to include stacks and globals in
the format line, and prints lastStackScan for "# MB stacks" instead of
maxStackScan, which is more accurate.
Fixes #54649.
Change-Id: Ibff2c390c9c9bf2b24b5b4e98ca346cc98d7cb2e
Reviewed-on: https://go-review.googlesource.com/c/go/+/425366
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Michael Pratt <mpratt@google.com>