eslint react-hooks/rulesOfHooks: add rule to check for non-function return from useEffect about react

[vkurchatkin]

This has nothing to do with rules of hooks. What you want is type checking, that is what TypeScript is for

[jlbooker]

@vkurchatkin Yes, a realize a full and complete solution to this requires a type checking system to fully evaluate the return type. However, it seems there are at least a few cases we could check for with lint rules, and that would handle 95% of the basic cases. For example, I came upon uses return "none"; and return null;, which are clearly not allowed and easily caught by a lint rule. Anything other than a bare return, undefined, or an arrow function is probably an error.