cmd/tailscaled: unify the two Windows paths + separate IPN server path

tailscaled on Windows had two entirely separate start-up paths for running
as a service vs in the foreground. It's been causing problems for ages.
This unifies the two paths, making them be the same as the path used
for every other platform.

Also, it uses the new async LocalBackend support in ipnserver.Server
so the Server can start serving HTTP immediately, even if tun takes
awhile to come up.

Updates #6535

Change-Id: Icc8c4f96d4887b54a024d7ac15ad11096b5a58cf
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tstest/integration/tailscaled_deps_test_darwin.go

@@ -36,6 +36,7 @@ import (
 	_ "tailscale.com/safesocket"
 	_ "tailscale.com/smallzstd"
 	_ "tailscale.com/ssh/tailssh"
+	_ "tailscale.com/syncs"
 	_ "tailscale.com/tailcfg"
 	_ "tailscale.com/tsweb"
 	_ "tailscale.com/types/flagtype"

tstest/integration/tailscaled_deps_test_freebsd.go

@@ -36,6 +36,7 @@ import (
 	_ "tailscale.com/safesocket"
 	_ "tailscale.com/smallzstd"
 	_ "tailscale.com/ssh/tailssh"
+	_ "tailscale.com/syncs"
 	_ "tailscale.com/tailcfg"
 	_ "tailscale.com/tsweb"
 	_ "tailscale.com/types/flagtype"

tstest/integration/tailscaled_deps_test_linux.go

@@ -36,6 +36,7 @@ import (
 	_ "tailscale.com/safesocket"
 	_ "tailscale.com/smallzstd"
 	_ "tailscale.com/ssh/tailssh"
+	_ "tailscale.com/syncs"
 	_ "tailscale.com/tailcfg"
 	_ "tailscale.com/tsweb"
 	_ "tailscale.com/types/flagtype"

tstest/integration/tailscaled_deps_test_openbsd.go

@@ -35,6 +35,7 @@ import (
 	_ "tailscale.com/paths"
 	_ "tailscale.com/safesocket"
 	_ "tailscale.com/smallzstd"
+	_ "tailscale.com/syncs"
 	_ "tailscale.com/tailcfg"
 	_ "tailscale.com/tsweb"
 	_ "tailscale.com/types/flagtype"

tstest/integration/tailscaled_deps_test_windows.go

@@ -16,6 +16,7 @@ import (
 	_ "golang.org/x/sys/windows/svc"
 	_ "golang.org/x/sys/windows/svc/eventlog"
 	_ "golang.org/x/sys/windows/svc/mgr"
+	_ "golang.zx2c4.com/wireguard/tun"
 	_ "golang.zx2c4.com/wireguard/windows/tunnel/winipcfg"
 	_ "tailscale.com/cmd/tailscaled/childproc"
 	_ "tailscale.com/control/controlclient"
@@ -41,6 +42,7 @@ import (
 	_ "tailscale.com/paths"
 	_ "tailscale.com/safesocket"
 	_ "tailscale.com/smallzstd"
+	_ "tailscale.com/syncs"
 	_ "tailscale.com/tailcfg"
 	_ "tailscale.com/tsweb"
 	_ "tailscale.com/types/flagtype"