This PR does two things:

1. I moved `package.json` into the root directory. Why? We are using `npx` from the `Makefile` which is executing usually under the root directory. If we install `node_modules` in `src/js` then these invocations don't see `node_modules` and install an extra copy of the packages. So we want `node_modules` in the root directory. node wants to put `node_modules` in the same directory as `package.json` hence I moved `package.json`. I also updated the build rules so that any recipe that uses `npx` has a dependency on `node_modules/.installed`.
2. We invoke `file_packager.py` from both the Makefile (in two places) and from `build_pkg`. There has been some drift in which options are applied in the two places. I extracted the common options and the task of locating the `file_packager.py` script into `tools/file_packager.sh`. I also shortened the make rules for `distutils.data` and `test.data` and made some minor updates to the dev docs about `file_packager.py`.
MAINT Improvements to node and file_packager invocations. This PR does two things:

1. I moved `package.json` into the root directory. Why? We are using `npx` from the `Makefile` which is executing usually under the root directory. If we install `node_modules` in `src/js` then these invocations don't see `node_modules` and install an extra copy of the packages. So we want `node_modules` in the root directory. node wants to put `node_modules` in the same directory as `package.json` hence I moved `package.json`. I also updated the build rules so that any recipe that uses `npx` has a dependency on `node_modules/.installed`.
2. We invoke `file_packager.py` from both the Makefile (in two places) and from `build_pkg`. There has been some drift in which options are applied in the two places. I extracted the common options and the task of locating the `file_packager.py` script into `tools/file_packager.sh`. I also shortened the make rules for `distutils.data` and `test.data` and made some minor updates to the dev docs about `file_packager.py`.
# Python API

Backward compatibility of the API is not guaranteed at this point.

**Javascript Modules**

By default there are two Javascript modules. More can be added with
{any}`pyodide.registerJsModule`. You can import these modules using the Python
``import`` statement in the normal way.

```{eval-rst}
.. list-table::

   *  - ``js``
      - The global Javascript scope.
   *  - :js:mod:`pyodide_js <pyodide>`
      - The Javascript Pyodide module.
```

```{eval-rst}
.. currentmodule:: pyodide

.. automodule:: pyodide
   :members:
   :autosummary:
   :autosummary-no-nesting:
```

# Python API

Backward compatibility of the API is not guaranteed at this point.

**Javascript Modules**

By default there are two Javascript modules. More can be added with
{any}`pyodide.registerJsModule`. You can import these modules using the Python
``import`` statement in the normal way.

```{eval-rst}
.. list-table::

   *  - ``js``
      - The global Javascript scope.
   *  - :js:mod:`pyodide_js <pyodide>`
      - The Javascript Pyodide module.
```

```{eval-rst}
.. currentmodule:: pyodide

.. automodule:: pyodide
   :members:
   :autosummary:
   :autosummary-no-nesting:
```
