runtime,runtime/metrics: add object size distribution metrics
This change adds metrics for the distribution of objects allocated and
freed by size, mirroring MemStats' BySize field.
For #37112.
Change-Id: Ibaf1812da93598b37265ec97abc6669c1a5efcbf
Reviewed-on: https://go-review.googlesource.com/c/go/+/247045
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Michael Knyszek <mknyszek@google.com> Reviewed-by: Michael Pratt <mpratt@google.com>