runtime: move pcvalue cache to M

Currently, the pcvalue cache is stack allocated for each operation
that needs to look up a lot of pcvalues. It's not always clear where
to put it, a lot of the time we just pass a nil cache, it doesn't get
reused across operations, and we put a surprising amount of effort
into threading these caches around.

This CL moves it to the M, where it can be long-lived and used by all
pcvalue lookups, and we don't have to carefully thread it across
operations.

Change-Id: I675e583e0daac887c8ef77a402ba792648d96027
Reviewed-on: https://go-review.googlesource.com/c/go/+/515276
Run-TryBot: Austin Clements <austin@google.com>
Auto-Submit: Austin Clements <austin@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>

src/runtime/runtime2.go

@@ -611,6 +611,9 @@ type m struct {
 	// Whether this is a pending preemption signal on this M.
 	signalPending atomic.Uint32
 
+	// pcvalue lookup cache
+	pcvalueCache pcvalueCache
+
 	dlogPerM
 
 	mOS