enable conditional exports

[yaacovCR]

depends on #4446

before:

i.e. importing from esm gives you cjs

after:

we have conditional exports, and it looks like nothing has changed.....

BUT:

Any version of Node honoring the module-sync condition i.e. where require(esm) is enabled will load ESM both when imported and required, i.e. ^20.19.0 || ^22.12.0 || >=23.0.0, i.e. latest versions of all current Node.JS releases.

We have been delaying this for some time secondary to dual-package-hazard concerns, but this looks like we can release ESM to the broader community via package exports while retaining whatever legacy CJS build we might need for those environments that need it => looking at you Jest.

We can look into whether we want to drop cjs support entirely as a follow-on PR => see #4437

[yaacovCR]

The secret sauce is here:

https://github.com/yaacovCR/graphql-js/blob/dual/resources/build-npm.ts#L204-L221

function buildExports(filepath: string): ConditionalExports {
  const { dir, name } = path.parse(filepath);
  const base = `./${path.join(dir, name)}`;
  return {
    types: {
      module: `${base}.d.mts`,
      'module-sync': `${base}.d.mts`,
      node: `${base}.d.ts`,
      require: `${base}.d.ts`,
      default: `${base}.d.mts`,
    },
    module: `${base}.mjs`,
    'module-sync': `${base}.mjs`,
    node: `${base}.js`,
    require: `${base}.js`,
    default: `${base}.mjs`,
  };
}

Based on:

nodejs/node#52174

[yaacovCR]

This solves node -- but what about bun and deno:

Bun seems to support: ["bun", "node", "require", "import", "default"] so our current scheme would also seem to give cjs.
https://bun.sh/docs/runtime/modules#importing-packages
oven-sh/bun#20768

Deno seems to support: ["deno", "node", "import", "default"] so our current scheme would seem to give cjs.
https://docs.deno.com/runtime/fundamentals/node/#conditional-exports
denoland/deno#29970

We would probably need to add custom conditions for bun and deno.

[yaacovCR]

With further testing, it seems that require(esm) on deno, at least how I am using it, does not honor the deno condition? So we can set deno to cjs or just drop it, because deno does consistently honor the node condition….