Harness primitive for testing expected crashes / uncaught exceptions

首先阅读 test_exception/testFinalizerException.js 和 test_fatal，以比较它们对 subprocess 的预期。围绕提议的 expectCrash 形式设计由实现者提供的 harness，包括 stderr 匹配以及基于 exception 或 signal 的终止。当两个受影响的测试都能使用 helper，并且仍能验证预期的 crash 结果时，即视为完成。

Problem

Several upstream Node.js tests verify behavior that causes the process to exit abnormally — uncaught exceptions from finalizers, fatal errors, etc. These tests use a subprocess pattern:

1. Spawn a child process that loads the addon and triggers the crash
2. Assert on the child's exit code and stderr output

The CTS currently has no equivalent harness primitive for this pattern.

Affected tests

• test_exception/testFinalizerException.js (js-native-api) — finalizer throws during GC, expects process exit with "Error during Finalize" on stderr
• test_fatal (node-api) — calls napi_fatal_error, expects process abort with specific message

Proposed solution

Add a harness helper that runs a code snippet in a subprocess and asserts on the outcome:

// Possible API shape:
await expectCrash({
  code: () => {
    const addon = loadAddon('test_exception');
    addon.createExternal();
    // trigger GC...
  },
  stderr: /Error during Finalize/,
  exitCode: (code) => code !== 0,
});

Each implementor would provide the subprocess execution mechanism (e.g., Node.js would use child_process.spawnSync).

Considerations

• The helper needs to be implementor-provided since subprocess APIs are runtime-specific
• The test code to run in the subprocess may need access to loadAddon and other CTS globals
• Some crashes are signal-based (SIGABRT from napi_fatal_error) vs exception-based — the helper should handle both