tools: move eslint from tools to tools/node_modules

This is required because we need to add the babel-eslint dependency
and it has to be able to resolve "eslint".
babel-eslint is required to support future ES features such as async
iterators and import.meta.

Refs: https://github.com/nodejs/node/pull/17755
PR-URL: https://github.com/nodejs/node/pull/17820


Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>