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/TailMac.xcodeproj/xcuserdata/jnobels.xcuserdatad/xcschemes/xcschememanagement.plist

@@ -0,0 +1,37 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>SchemeUserState</key>
+	<dict>
+		<key>VMRunner.xcscheme_^#shared#^_</key>
+		<dict>
+			<key>orderHint</key>
+			<integer>2</integer>
+		</dict>
+		<key>host.xcscheme_^#shared#^_</key>
+		<dict>
+			<key>orderHint</key>
+			<integer>1</integer>
+		</dict>
+		<key>tailmac.xcscheme_^#shared#^_</key>
+		<dict>
+			<key>orderHint</key>
+			<integer>0</integer>
+		</dict>
+	</dict>
+	<key>SuppressBuildableAutocreation</key>
+	<dict>
+		<key>8FDABC39270D1DC600D7FC60</key>
+		<dict>
+			<key>primary</key>
+			<true/>
+		</dict>
+		<key>8FDABC58270D1FFE00D7FC60</key>
+		<dict>
+			<key>primary</key>
+			<true/>
+		</dict>
+	</dict>
+</dict>
+</plist>