feature/portlist: pull portlist service porting into extension, use eventbus

And yay: tsnet (and thus k8s-operator etc) no longer depends on
portlist! And LocalBackend is smaller.

Removes 50 KB from the minimal binary.

Updates #12614

Change-Id: Iee04057053dc39305303e8bd1d9599db8368d926
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

feature/buildfeatures/feature_portlist_disabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build ts_omit_portlist
+
+package buildfeatures
+
+// HasPortList is whether the binary was built with support for modular feature "Optionally advertise listening service ports".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_portlist" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasPortList = false

feature/buildfeatures/feature_portlist_enabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build !ts_omit_portlist
+
+package buildfeatures
+
+// HasPortList is whether the binary was built with support for modular feature "Optionally advertise listening service ports".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_portlist" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasPortList = true