fix(develop): add blank .css to ensure mini-css-extract-plugin always has something to extract

[pieh]

Description

This handle 2 issues:

1. Resource interpreted as Stylesheet but transferred with MIME type text/html: "http://localhost:8000/commons.css".

When there is no css, we add commons.css link but we don't actually generate it, so we serve our index.html instead for that request, which cause warning as above + generally is wonky

2. In develop when you remove "last" .css import - the styles stay behind, because commons.css is not "regenerated" but it continue to exist in webpack-dev-middleware in-memory filesystem. Having that blank .css import actually ensure that when user removes their last .css commons.css updates (to empty file), meaning that we don't leave stale styles behind

Related Issues

[ch25434]