Fix the scoping of our ESLint rules (#13558)

* Scope ESLint to src/client/pythonEnvironments
* Handle ipywidgets multi-root workspace
* Ignore build/, un-ignore test/pythonEnvironments
* ignore pythonEnvironments/ for Prettier
* Move newline around
* Use max-classes-per-file default
* Disable ESLint on all existing js, jsx, ts and tsx files

Author: kimadeline