syncs: add Mutex/RWMutex alias/wrappers for future mutex debugging

Updates #17852

Change-Id: I477340fb8e40686870e981ade11cd61597c34a20
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

util/syspolicy/rsop/change_callbacks.go

@@ -9,6 +9,7 @@ import (
 	"sync"
 	"time"
 
+	"tailscale.com/syncs"
 	"tailscale.com/util/set"
 	"tailscale.com/util/syspolicy/internal/loggerx"
 	"tailscale.com/util/syspolicy/pkey"
@@ -70,7 +71,7 @@ func (c PolicyChange) HasChangedAnyOf(keys ...pkey.Key) bool {
 // policyChangeCallbacks are the callbacks to invoke when the effective policy changes.
 // It is safe for concurrent use.
 type policyChangeCallbacks struct {
-	mu  sync.Mutex
+	mu  syncs.Mutex
 	cbs set.HandleSet[PolicyChangeCallback]
 }