Add universal macOS release build with exported opening verification

Makefile

@@ -191,6 +191,13 @@ test-transport-comparison:
 
 # Check the actual shipped data outside this checkout, including first build.
 WINDOWS_PCK ?= build/windows/TheTree.pck
+MACOS_APP ?= build/macos/TheTree.app
+.PHONY: export-macos
+export-macos:
+	mkdir -p build/macos
+	$(GODOT) --headless --path . --export-release "macOS" "$(MACOS_APP)"
+	python3 tools/verify_exported_opening.py "$(MACOS_APP)/Contents/Resources/The Tree.pck" --godot "$(GODOT)"
+
 .PHONY: test-exported-opening
 test-exported-opening:
 	python3 tools/verify_exported_opening.py "$(WINDOWS_PCK)" --godot "$(GODOT)"