add build script for codemirror package

packages/codemirror/vite.config.js

@@ -0,0 +1,19 @@
+import { defineConfig } from 'vite';
+import { dependencies } from './package.json';
+import { resolve } from 'path';
+
+// https://vitejs.dev/config/
+export default defineConfig({
+  plugins: [],
+  build: {
+    lib: {
+      entry: resolve(__dirname, 'codemirror.mjs'),
+      formats: ['es', 'cjs'],
+      fileName: (ext) => ({ es: 'index.mjs', cjs: 'index.js' }[ext]),
+    },
+    rollupOptions: {
+      external: [...Object.keys(dependencies)],
+    },
+    target: 'esnext',
+  },
+});