Support conditional exports without export package.json

[xiaoxiangmoe]

import * as utils from 'utils-ts'
console.log(utils)

it will throw an error:

Error: ENOENT: no such file or directory, stat '/Users/foobar/my-react-project/node_modules/utils-ts/dist/utils-ts.js'

The package.json of utils-ts is:

{
  "name": "utils-ts",
  "version": "0.1.0-alpha.3",
  "types": "./dist/utils-ts.d.ts",
  "main": "./dist/utils-ts.cjs",
  "module": "./dist/utils-ts.mjs",
  "exports": {
    ".": {
      "import": "./dist/utils-ts.mjs",
      "require": "./dist/utils-ts.cjs",
      "default": "./dist/utils-ts.cjs"
    }
  }
}

---

vite/src/node/utils/pathUtils.ts

Lines 6 to 7 in 91f829d

	export const resolveFrom = (root: string, id: string) =>
	require.resolve(id, { paths: [root] })

vite/src/node/resolver.ts

Lines 179 to 183 in 4637556

	let pkgPath
	try {
	// see if the id is a valid package name
	pkgPath = resolveFrom(root, `${id}/package.json`)
	} catch (e) {}

It will throw an Error for library utils-ts:

Uncaught:
Error [ERR_PACKAGE_PATH_NOT_EXPORTED]: Package subpath './package.json' is not defined by "exports" in /Users/foobar/my-react-project/node_modules/utils-ts/package.json

---

Maybe we could build vite into mjs and use --experimental-import-meta-resolve.

Also, we should support paths rather than root, because ./src has no node_modules dir.