This is in effect a partial rollback of PR #7822.
This should solve issues encountered by users of bunders that don't
support exports at all (e.g. browserify) as well as ones that don't
support it in certain circumstances (e.g., when using webpack's
resolve.alias configuration option to alias 'blockly' to
'node_modules/blockly', as we formerly did in most plugins, which
causes webpack to ignore blockly's package.json entirely).
Assumptions:
- Such bundlers will _completely_ ignore the exports declaration.
- The bundles are intended to be used in a browser—or at least not
in node.js—so the core entrypoint never needs to route to
core-node.js. This is reasonable since there's little reason to
bundle code for node.js, and node.js has supported the exports
clause since at least v12, considerably older than any version of
node.js we officially support.
- It suffices to provide only a CJS entrypoint (because we can only
provide CJS or ESM, not both. (We could in future switch to
providing only an ESM entrypoint instead, though.)
* fix: loading messages in the browser
* chore: fix comment
* fix: change unwrapped message files to write to a new object, rather than Blockly.Msg
* fix: fixup exports
* fix: PR comments
* fix: change to use for-in loop
* fix: ES6 compatibility and formatting
