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/Assets.xcassets/AccentColor.colorset/Contents.json

@@ -0,0 +1,11 @@
+{
+  "colors" : [
+    {
+      "idiom" : "universal"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}

tstest/tailmac/Swift/Host/Assets.xcassets/AppIcon.appiconset/Contents.json

@@ -0,0 +1,58 @@
+{
+  "images" : [
+    {
+      "idiom" : "mac",
+      "scale" : "1x",
+      "size" : "16x16"
+    },
+    {
+      "idiom" : "mac",
+      "scale" : "2x",
+      "size" : "16x16"
+    },
+    {
+      "idiom" : "mac",
+      "scale" : "1x",
+      "size" : "32x32"
+    },
+    {
+      "idiom" : "mac",
+      "scale" : "2x",
+      "size" : "32x32"
+    },
+    {
+      "idiom" : "mac",
+      "scale" : "1x",
+      "size" : "128x128"
+    },
+    {
+      "idiom" : "mac",
+      "scale" : "2x",
+      "size" : "128x128"
+    },
+    {
+      "idiom" : "mac",
+      "scale" : "1x",
+      "size" : "256x256"
+    },
+    {
+      "idiom" : "mac",
+      "scale" : "2x",
+      "size" : "256x256"
+    },
+    {
+      "idiom" : "mac",
+      "scale" : "1x",
+      "size" : "512x512"
+    },
+    {
+      "idiom" : "mac",
+      "scale" : "2x",
+      "size" : "512x512"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}

tstest/tailmac/Swift/Host/Assets.xcassets/Contents.json

@@ -0,0 +1,6 @@
+{
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}