feat(build)!: Introduce ESM entrypoints

[cpcallen]

The basics

• I validated my changes

The details

Resolves

Work towards #7449

Proposed Changes

Introduce an import conditional export for each of the entrypoints (blockly, blockly/core, blockly/blocks, blockly/javascript, etc., blockly/msg/en, blockly/msg/fr, etc.), and point these at wrappers created by build_tasks.js
that import the corresponding index.js / <chunk>_compressed.js / msg/<lang>.js CJS module and export its named exports.

Reason for Changes

Providing ESM entrypoints, even ones that are just wrappers of the existing CJS entrypoints, is the first step towards publishing Blockly as a pure-ESM package.

Test Coverage

• Verified that npm test runs successfully.
• Verified that import * as … from 'blockly/…' works correctly and as expected when run in node.js.
• Verified that npm test runs successfully in blockly-samples rc/v11.0.0 branch, when linked against Blockly from this branch.

No changes to manual test procedures expected.

Documentation

• Release notes should contain the breaking change notice below.
• We need to check our published documentation and code samples for any incorrect imports. (The blockly-samples repository has already been checked and fixed in the rc/v11.0.0 branch.)

Additional Information

The ESM entrypoints provided by this PR are unfortunately still not directly importable by browsers, hence not being a complete fix for #7449. This is due to them directly importing the CJS (actually UMD) modules, which is supported by node.js and most build tooling but not by browsers, which do not natively support CJS. It may be possible to fix this in a future commit by providing a require polyfill, but doing this in a way that is compatible with build tooling and does not re-introduce the dual package hazard is not straightforward.

BREAKING CHANGE:

Importing Blockly via

import Blockly from 'blockly';

(and similarly for the other entrypoints) has worked until now because most build tools (including webpack in particular)
fulfil the request for the default export of a CJS module by providing the module.exports object, rather than an explicitly-named default export as they would for an ES module.

Since core/blockly.ts (the notional entrypoint for blockly/core) and the other chunk entrypoints do not provide a default export, the wrappers created by this PR do not either.

Code of the above form will therefore break, and should be updated to use a wildcard:

import * as Blockly from 'blockly';

[cpcallen]

It might be helpful when reviewing to know that the generated wrappers have the form (e.g. blockly.mjs):

import Blockly from './blockly_compressed.js';
export const {
  ASTNode,
  BasicCursor,
  Block,
  // ...
  utils,
  zelos,
} = Blockly;