runtime: split out pointer/scalar metadata from heapArena
We're going to want to fork this data in the near future for a
GOEXPERIMENT, so break it out now.
Change-Id: Ia7ded850bb693c443fe439c6b7279dcac638512c
Reviewed-on: https://go-review.googlesource.com/c/go/+/537978 Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>