[Feature] Support native ESM explicitly in package.json

[snake-poison]

What problem does this feature solve?

Looks like the space and standards are moving towards ESM, it'd be cool if this library embraced that by switching to a package.json that embraces the latest best practices in multi-format support.

See:
Additional context about this issue:

• https://v3.nuxtjs.org/concepts/esm/#what-kinds-of-problems-can-there-be
• ERR_MODULE_NOT_FOUND : echarts\core only during SSG Build antfu-collective/vite-ssg#201

What does the proposed API look like?

package.json would include the type and exports options:

  "type": "module",
  "exports": {
    ".": {
      "require": "./dist/echarts.js",
      "import": "./dist/echarts.esm.js",
      "types": "./index.d.ts"
    },
    "./core": {
      "import": "./core.js",
      "types": "./core.d.ts"
    },
    "./renderers": {
      "import": "./renderers.js",
      "types": "./renderers.d.ts"
    },
    "./charts": {
      "import": "./charts.js",
      "types": "./charts.d.ts"
    },
    "./components": {
      "import": "./components.js",
      "types": "./components.d.ts"
    },
     "./features": {
      "import": "./features.js",
      "types": "./features.d.ts"
    }
  },

[snake-poison]

The suggestion here would break cjs builds. Closing this as that is probably not a good idea....

I will come back with a PR to update the build process to create .mjs and .cjs files.