Convert build scripts to ESM (#38984)

build/banner.mjs

@@ -0,0 +1,20 @@
+import fs from 'node:fs/promises'
+import path from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url))
+
+const pkgJson = path.join(__dirname, '../package.json')
+const pkg = JSON.parse(await fs.readFile(pkgJson, 'utf8'))
+
+const year = new Date().getFullYear()
+
+function getBanner(pluginFilename) {
+  return `/*!
+  * Bootstrap${pluginFilename ? ` ${pluginFilename}` : ''} v${pkg.version} (${pkg.homepage})
+  * Copyright 2011-${year} ${pkg.author}
+  * Licensed under MIT (https://github.com/twbs/bootstrap/blob/main/LICENSE)
+  */`
+}
+
+export default getBanner