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/Makefile

@@ -0,0 +1,23 @@
+XCPRETTIFIER := xcpretty
+ifeq (, $(shell which $(XCPRETTIFIER)))
+	XCPRETTIFIER := cat
+endif
+
+.PHONY: tailmac
+tailmac:
+	xcodebuild -scheme tailmac -destination 'platform=macOS,arch=arm64' -derivedDataPath build -configuration Release build | $(XCPRETTIFIER)
+	cp -r ./build/Build/Products/Release/tailmac ./bin/tailmac
+
+.PHONY: host
+host:
+	xcodebuild -scheme host -destination 'platform=macOS,arch=arm64'  -derivedDataPath build -configuration Release build | $(XCPRETTIFIER)
+	cp -r ./build/Build/Products/Release/Host.app ./bin/Host.app
+
+.PHONY: clean
+clean:
+	rm -rf ./bin
+	rm -rf ./build
+	mkdir -p ./bin
+
+.PHONY: all
+all: clean tailmac host