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`.
# js/pyodide

The Javascript code in this folder is responsible for the following tasks:

1. Defines the public Javascript API
   - Package loading code to allow loading of other Python packages.
   - Can load micropip.py to bootstrap loading of pure Python wheels
2. Loads the CPython interpreter and the core/pyodide emscripten application
   which embeds the interpreter.
3. Injects the js/pyodide Javascript API into sys.modules. This is the final
   runtime dependency for core/pyodide & py/pyodide, so after this step the
   interpreter is fully up and running.

# js/pyodide

The Javascript code in this folder is responsible for the following tasks:

1. Defines the public Javascript API
   - Package loading code to allow loading of other Python packages.
   - Can load micropip.py to bootstrap loading of pure Python wheels
2. Loads the CPython interpreter and the core/pyodide emscripten application
   which embeds the interpreter.
3. Injects the js/pyodide Javascript API into sys.modules. This is the final
   runtime dependency for core/pyodide & py/pyodide, so after this step the
   interpreter is fully up and running.
