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- [x] Add new / update outdated documentation

---
name: Package request
about: Request a new Python package or a version update
title: ""
labels: new package request
assignees: ""
---

<!-- Important Note: You can install pure python package wheels through micropip.install(...) -->

## 🐍 Package Request

- Package Name and Version <!-- (e.g. pandas / latest) -->:
- Package URL <!--  (e.g. github link, PyPI link) -->:
- Package Dependencies that needs to be resolved first:

---
name: Package request
about: Request a new Python package or a version update
title: ""
labels: new package request
assignees: ""
---

<!-- Important Note: You can install pure python package wheels through micropip.install(...) -->

## 🐍 Package Request

- Package Name and Version <!-- (e.g. pandas / latest) -->:
- Package URL <!--  (e.g. github link, PyPI link) -->:
- Package Dependencies that needs to be resolved first:
