Replace 9,937 lines of inline Go struct test expectations in
tailscale_acl_compat_test.go with 215 JSON golden files in
testdata/acl_results/ACL-*.json and a ~400-line Go driver in
tailscale_acl_data_compat_test.go.
This matches the pattern used by the grants compat tests
(testdata/grant_results/GRANT-*.json + tailscale_grants_compat_test.go)
and the SSH compat tests (testdata/ssh_results/SSH-*.json +
tailscale_ssh_data_compat_test.go).
The JSON golden files contain the same test expectations as the
original Go file, preserving the Tailscale SaaS reference data.
The expectations are NOT adapted to match headscale current output —
they represent the target behavior.
Test count is preserved: 215 test cases (203 success + 12 error).
Updates #2180