tools: Symlink node_modules in project root

tools: Symlink node_modules in project root

NPM assumes quite strongly that it manages the project as a
whole and its package/lock files are located in the project
root.

While we somehow managed to keep the npm tooling in a subfolder,
this comes at the cost of breaking imports of additional modules.

This will become relevant when we update eslint to a supported
version, as we want to keep using the `junit` formatter in CI,
which has now been split out into a separate module.

So bite the bullet and make the node_modules folder available in
the project root.

On the plus side, having the node_modules folder in the project
root allows language servers in IDEs/editors to pick it up.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3929>