pyodide pack: Add support for packages installed with micropip

[rth]

Closes #4

The added logic is,

1. Try installing dependencies with loadPackage. If it fails, fallback to micropip
2. If micropip is installed, at the end of the application run, call micropip.freeze() and use the output as the new lockfile for finding the install URL of wheels downloaded from PyPI
3. Download PyPI wheels to node_modules/pyodide alongside wheels downloaded by loadPackage. This is maybe a non-optimal side effect of running pyodide pack but we should do PyPI wheel caching in node in any case.

This means however that micropip + packaging get budled unnecessarily. For now, given their relatively small size I will keep them.

Example of running pyodide pack examples/micropip_deps/app.py

┏━━━━┳━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━┳━━━━━━━━━━┳━━━━━━━━━━━━━┳━━━━━━━━━━━┓
┃ No ┃ Package                        ┃ All files ┃ .so libs ┃   Size (MB) ┃ Reduction ┃
┡━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━╇━━━━━━━━━━╇━━━━━━━━━━━━━╇━━━━━━━━━━━┩
│  0 │ stdlib                         │ 547 → 161 │          │ 2.25 → 0.82 │    63.6 % │
│  1 │ micropip-0.4.0-py3-none-any.w… │   33 → 28 │    0 → 0 │ 0.05 → 0.04 │    17.7 % │
│  2 │ packaging-23.1-py3-none-any.w… │   21 → 14 │    0 → 0 │ 0.05 → 0.04 │    24.1 % │
│  3 │ snowballstemmer-2.2.0-py2.py3… │   37 → 34 │    0 → 0 │ 0.08 → 0.08 │     3.2 % │
└────┴────────────────────────────────┴───────────┴──────────┴─────────────┴───────────┘
Wrote pyodide-package-bundle.zip with 0.17 MB (2.2% reduction)
[...]
Total output size (stdlib + packages): 0.99 MB (59.2% reduction)

[ryanking13]

Thanks! I guess we need some more strict tests for micropip.freeze() as we now use it here.