"fs" module needs propper return types and overloads

This needs real overloads and better return types than `any` https://github.com/adobe/cc-ext-uxp-types/blob/main/uxp/index.d.ts#L8956

At current state I have to write my own typings instead of using yours.

You could probably copy/paste some parts of NodeJS types: https://www.npmjs.com/package/@types/node?activeTab=code

Start at uxp/index.d.ts around line 8956 and compare the fs declarations with the relevant @types/node definitions. Update the module's any-based signatures with proper return types and overloads, so consumers no longer need to maintain their own typings.

Written by the indexing model from the issue text.