runtime: add lock rank partial-order edge between fin and mheap
finlock may be held across a write barrier, which could then acquire the
mheap lock. Notably, this occurs in the mp.unlockf write in gopark where
finlock is held by the finalizer goroutines and is going to sleep.
Fixes #42062.
Change-Id: Icf76637ae6fc12795436272633dca3d473780875
Reviewed-on: https://go-review.googlesource.com/c/go/+/263678
Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Dan Scales <danscales@google.com>