Description of axe import into Moodle

1/ Download the latest axe code somewhere (example /tmp/axe) using:

mkdir -p axe/node_modules
npm install --prefix axe axe-core --save-dev

Note down the version number displayed by the command, to update lib/thirdpartylibs.xml accordingly.

2/ Copy the following file to your local Moodle directory, to replace the old one:

cp axe/node_modules/axe-core/axe.min.js [PATH TO YOUR MOODLE]/lib/behat/axe/

3/ Run behat tests labelled with @accessibility and confirm they are passing with the new library version, or fix the failures
because the new version might raise issues that weren't detected previously:

php admin/tool/behat/cli/init.php --add-core-features-to-theme
php admin/tool/behat/cli/run.php --tags=@accessibility