Expose the default module resolver in a package

Currently we can access the default resolver when in a --loader loader. However we can't access this loader from a regular program. I'd like to propose exposing this function as a regular function that can be imported at runtime for use with vm.SourceTextModule to create in-process loaders.

For example:

import vm from 'vm';
import process from 'process';
import url from 'url';
import { resolver } from 'module';

const cwd = url.pathToFileURL(process.cwd() + '/');

class TestLoader {
  #cache = new Map();
  #realm = vm.createContext({});

  async #loadModule(url) {
    return new vm.SourceTextModule(await fsp.readFile(resolvedUrl, 'utf8'), {
      url: resolvedUrl,
      context: this.#realm,
    });
  }
  
  async #linker(module, specifier) {
    // --- Use node's resolution algorithm ---
    const resolvedUrl = resolver(module.url, specifier);
    if (this.#cache.has(resolvedUrl)) {
      return this.#cache.get(resolvedUrl);
    }
    const module = this.#loadModule(resolvedUrl);
    this.#cache.set(resolvedUrl, module);
    return module;
  }

  constructor() {
    // Setup test environment
    this.#realm.evaluate(`function deepEqual(a, b) { /* ... */ }`);
  }

  async runTest(file) {
    const module = this.#loadModule(resolver(cwd, file));
    await module.link((...args) => this.#linker(...args));
    module.instantiate();
    try {
      await module.evaluate();
      return { passed: true };
    } catch (error) {
      return { passed: false, error };
    }
  }
}

首先查看可用于 --loader loaders 的现有 resolver，以及示例中展示的 vm.SourceTextModule 链接流程。确定导入默认 resolver 所需的运行时 API 和模块入口点，然后验证它是否支持示例所示的进程内 loader 解析。