files add through spinx's app.add_js_file are added to body not the header.

[lukasturcani]

Hello,

I believe themes should insert header files added via app.add_js_file into the header. In furo my files get added to the body instead. This is an issue if an extension requires a setup script in the header.

For an example:

git clone https://github.com/lukasturcani/moldoc
# create a new venv with your favorite tool
pip install -e '.[dev]'
make -C tests html

Open tests/build/html/index.html.
Open developer tools and notice that files add with add_js_file are in the body section of the HTML not in the header
If you change the theme to alabaster or something else, you will notice that the files are in the header