Export PATH and ERRNO_CODES from Emscripten. ### Description

Fixes #2577 by exporting `PATH` and `ERRNO_CODES` from Emscripten

### Checklists

- [x] Add a [CHANGELOG](https://github.com/pyodide/pyodide/blob/main/docs/project/changelog.md) entry
- [x] Add / update tests
- [x] Add new / update outdated documentation

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name: Documentation improvement
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title: ""
labels: documentation
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## 📚 Documentation

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name: Documentation improvement
about: Improve or fix the documentation
title: ""
labels: documentation
assignees: ""
---

## 📚 Documentation

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For typos and doc fixes, please go ahead and:

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