cmd/tailscaled,ipn/{auditlog,ipnlocal},tsd: omit auditlog unless explicitly imported

In this PR, we update ipnlocal.LocalBackend to allow registering callbacks for control client creation
and profile changes. We also allow to register ipnauth.AuditLogFunc to be called when an auditable
action is attempted.

We then use all this to invert the dependency between the auditlog and ipnlocal packages and make
the auditlog functionality optional, where it only registers its callbacks via ipnlocal-provided hooks
when the auditlog package is imported.

We then underscore-import it when building tailscaled for Windows, and we'll explicitly
import it when building xcode/ipn-go-bridge for macOS. Since there's no default log-store
location for macOS, we'll also need to call auditlog.SetStoreFilePath to specify where
pending audit logs should be persisted.

Fixes #15394
Updates tailscale/corp#26435
Updates tailscale/corp#27012

Signed-off-by: Nick Khyl <nickk@tailscale.com>

cmd/k8s-operator/depaware.txt

@@ -814,7 +814,6 @@ tailscale.com/cmd/k8s-operator dependencies: (generated by github.com/tailscale/
         tailscale.com/internal/client/tailscale                      from tailscale.com/cmd/k8s-operator
         tailscale.com/internal/noiseconn                             from tailscale.com/control/controlclient
         tailscale.com/ipn                                            from tailscale.com/client/local+
-        tailscale.com/ipn/auditlog                                   from tailscale.com/ipn/ipnlocal+
         tailscale.com/ipn/conffile                                   from tailscale.com/ipn/ipnlocal+
      💣 tailscale.com/ipn/desktop                                    from tailscale.com/ipn/ipnlocal+
      💣 tailscale.com/ipn/ipnauth                                    from tailscale.com/ipn/ipnlocal+

cmd/tailscaled/depaware.txt

@@ -271,7 +271,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/hostinfo                                       from tailscale.com/client/web+
         tailscale.com/internal/noiseconn                             from tailscale.com/control/controlclient
         tailscale.com/ipn                                            from tailscale.com/client/local+
-        tailscale.com/ipn/auditlog                                   from tailscale.com/ipn/ipnlocal+
+   W    tailscale.com/ipn/auditlog                                   from tailscale.com/cmd/tailscaled
         tailscale.com/ipn/conffile                                   from tailscale.com/cmd/tailscaled+
      💣 tailscale.com/ipn/desktop                                    from tailscale.com/cmd/tailscaled+
      💣 tailscale.com/ipn/ipnauth                                    from tailscale.com/ipn/ipnlocal+

cmd/tailscaled/tailscaled_windows.go

@@ -44,6 +44,7 @@ import (
 	"golang.zx2c4.com/wireguard/windows/tunnel/winipcfg"
 	"tailscale.com/drive/driveimpl"
 	"tailscale.com/envknob"
+	_ "tailscale.com/ipn/auditlog"
 	"tailscale.com/ipn/desktop"
 	"tailscale.com/logpolicy"
 	"tailscale.com/logtail/backoff"