We are pushing pyodide_build to PyPI as a Python package, but for now,
installing pyodide_build from PyPI (i.e. pip install pyodide_build`) is almost
useless because:
there are bunch of hard-coded paths (e.g. Path(__file__).parents[2]),
its dependencies are not specified in setup.cfg.
This PR is for mitigating this situation by removing hard-coded paths and
adding tests, and is also a preparation for our new CLI
(https://github.com/pyodide/pyodide/issues/1977).
The installation is very fast, and this avoids having two copies of node
around. In particular, this avoids the need to monkey-patch uglify-js to
use the system node.
This can be further streamlined when #792 is merged
Gyeongjae Choi