fixes #4398

- fixes API documentation for all of these (and `module:lib/cli.main`) via JSDoc aliasing
- aliases `lib/cli/cli.js` to `module:lib/cli`; `module:lib/cli/cli` is no longer a thing
- the `lib/cli/options.js` and `lib/cli/lookup-files.js` _modules_ (not necessarily their _contents_) are now private

example usage:

```js
const {loadRc, loadPkgRc, loadOptions, lookupFiles} = require('mocha/lib/cli');
```

lookupFiles() broke (moved) in version v8.1.0, this returns it and issues a soft deprecation warning.
in the browser, this function should not be called, but if it is, an `ERR_MOCHA_UNSUPPORTED` `Error` is thrown