Introduces code-no-deep-import-of-internal

[hediet]

This ESLint rule makes sure only siblings of "internal" source code folders can import into it (so they can either use it directly or re-export public API).

This (usually) means that an import like this is not allowed:

import { autorunWithStore, debouncedObservable, derived } from '../../../../base/common/observableInternal/base.js';

...whereas this import is allowed:

import { autorunWithStore, debouncedObservable, derived } from './observableInternal/base.js';