chore(build)!: drop cjs api

[brc-dd]

BREAKING CHANGE!

Drops Node CJS API. It is recommended to use

import {} from vitepress

instead of

const {} = require('vitepress')

and "type": "module" at the nearest package.json or .mjs/.mts extension for defining config (or other files where vitepress' node API is being used).

Trying to use CJS build will yield error:

"vitepress" resolved to an ESM file. ESM file cannot be loaded by `require`. See http://vitejs.dev/guide/troubleshooting.html#this-package-is-esm-only for more details. [plugin externalize-deps]

...

  The plugin "externalize-deps" was triggered by this import

    .vitepress/config.js:1:281:
      1 │ ...foo/.vitepress/config.js";const __vite_injected_original_import_meta_url = "file:///Users/brc-dd/foo/.vitepress/config.js";import { defineConfig } from 'vitepress'
        ╵                                                                                                                                                            ~~~~~~~~~~~

failed to load config from /Users/brc-dd/foo/.vitepress/config.js

The link in the error message should be sufficient for resolving most cases. In case of any issues, post it in #2703 itself. That issue won't be locked.

closes #2703

attw results

"vitepress"

node10: 🟢 
node16 (from CJS): ⚠️ ESM (dynamic import only)
node16 (from ESM): 🟢 (ESM)
bundler: 🟢 

***********************************

"vitepress/package.json"

node10: 🟢 (JSON)
node16 (from CJS): 🟢 (JSON)
node16 (from ESM): 🟢 (JSON)
bundler: 🟢 (JSON)

***********************************

"vitepress/client"

node10: 🟢 
node16 (from CJS): ⚠️ ESM (dynamic import only)
node16 (from ESM): 🟢 (ESM)
bundler: 🟢 

***********************************

"vitepress/theme"

node10: 🟢 
node16 (from CJS): ⚠️ ESM (dynamic import only)
node16 (from ESM): 🟢 (ESM)
bundler: 🟢 

***********************************

"vitepress/theme-without-fonts"

node10: 🟢 
node16 (from CJS): ⚠️ ESM (dynamic import only)
node16 (from ESM): 🟢 (ESM)
bundler: 🟢 

***********************************

[brc-dd]

/cc @bluwy @benmccann

[userquin]

Maybe we should add migration guide in readme and/or docs