fix: make package.json 'exports' work with typescript moduleResolution: 'bundler'

[stackia]

When importing antlr4 from a typescript project with moduleResolution: "bundler", typescript will fail to resolve the .d.ts provided by antlr4. That's because typescript tries to resolve the exports with condition ['types', 'import', 'default'] which does't match any of our declared exports.

Change the browser condition to default solves the issue. It's also recommended in Node.js doc:

When using environment branches, always include a "default" condition where possible. Providing a "default" condition ensures that any unknown JS environments are able to use this universal implementation, which helps avoid these JS environments from having to pretend to be existing environments in order to support packages with conditional exports. For this reason, using "node" and "default" condition branches is usually preferable to using "node" and "browser" condition branches.