Cannot import message files with filename that contain hyphens in v11

[devilhyt]

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Description

An error occurs when importing message files with filenames that contain hyphens (en-gb, zh-hant, etc).

In v11, a script for building message files was updated (#8091). The code below reveals that we directly use the filenames from msg/json/*.json to name the default export object.

blockly/scripts/gulpfiles/build_tasks.js

Lines 658 to 688 in 9519333

	/**
	* This task builds the ESM wrappers used by the langfiles "import"
	* entrypoints declared in package.json.
	*/
	async function buildLangfileShims() {
	// Create output directory.
	fs.mkdirSync(path.join(RELEASE_DIR, 'msg'), {recursive: true});
	// Get the names of the exports from the langfile by require()ing
	// msg/messages.js and letting it mutate the (global) Blockly.Msg.
	// (We have to do it this way because messages.js is a script and
	// not a CJS module with exports.)
	globalThis.Blockly = {Msg: {}};
	require('../../msg/messages.js');
	const exportedNames = Object.keys(globalThis.Blockly.Msg);
	delete globalThis.Blockly;
	await Promise.all(getLanguages().map(async (lang) => {
	// Write an ESM wrapper that imports the CJS module and re-exports
	// its named exports.
	const cjsPath = `./${lang}.js`;
	const wrapperPath = path.join(RELEASE_DIR, 'msg', `${lang}.mjs`);
	await fsPromises.writeFile(wrapperPath,
	`import ${lang} from '${cjsPath}';
	export const {
	${exportedNames.map((name) => ` ${name},`).join('\n')}
	} = ${lang};
	`);
	}));
	}

However, hyphens are not legal in javascript names, which seems to be the root cause of the issue.

Reproduction steps

1. Get Blockly through Create-package script.
2. Import message files in index.js (ex: en-gb).
   import * as enGb from 'blockly/msg/en-gb';

Stack trace

ERROR in ./node_modules/blockly/msg/en-gb.mjs 1:9
Module parse failed: Unexpected token (1:9)
You may need an appropriate loader to handle this file type, currently no loaders are configured to process this file. See https://webpack.js.org/concepts#loaders
> import en-gb from './en-gb.js';
| export const {
|   LOGIC_HUE,
 @ ./src/index.js 8:0-42 16:18-22

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