tstest/tailmac: add customized macOS virtualization tooling (#13146)

updates tailcale/corp#22371

Adds custom macOS vm tooling.  See the README for
the general gist, but this will spin up VMs with unixgram
capable network interfaces listening to a named socket,
and with a virtio socket device for host-guest communication.

We can add other devices like consoles, serial, etc as needed.

The whole things is buildable with a single make command, and
everything is controllable via the command line using the TailMac
utility.

This should all be generally functional but takes a few shortcuts
with error handling and the like.  The virtio socket device support
has not been tested and may require some refinement.

Signed-off-by: Jonathan Nobels <jonathan@tailscale.com>

tstest/tailmac/Swift/Host/AppDelegate.swift

@@ -0,0 +1,52 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+import Cocoa
+import Foundation
+import Virtualization
+
+class AppDelegate: NSObject, NSApplicationDelegate  {
+    @IBOutlet var window: NSWindow!
+
+    @IBOutlet weak var virtualMachineView: VZVirtualMachineView!
+
+    var runner: VMController!
+
+    func applicationDidFinishLaunching(_ aNotification: Notification) {
+        DispatchQueue.main.async { [self] in
+            runner = VMController()
+            runner.createVirtualMachine()
+            virtualMachineView.virtualMachine = runner.virtualMachine
+            virtualMachineView.capturesSystemKeys = true
+
+            // Configure the app to automatically respond to changes in the display size.
+            virtualMachineView.automaticallyReconfiguresDisplay = true
+
+            let fileManager = FileManager.default
+            if fileManager.fileExists(atPath: config.saveFileURL.path) {
+                print("Restoring virtual machine state from \(config.saveFileURL)")
+                runner.restoreVirtualMachine()
+            } else {
+                print("Restarting virtual machine")
+                runner.startVirtualMachine()
+            }
+
+        }
+    }
+
+    func applicationShouldTerminateAfterLastWindowClosed(_ sender: NSApplication) -> Bool {
+        return true
+    }
+
+    func applicationShouldTerminate(_ sender: NSApplication) -> NSApplication.TerminateReply {
+        if runner.virtualMachine.state == .running {
+            runner.pauseAndSaveVirtualMachine(completionHandler: {
+                sender.reply(toApplicationShouldTerminate: true)
+            })
+
+            return .terminateLater
+        }
+
+        return .terminateNow
+    }
+}