Optionally allow extending objects as a top-level side-effect

[ericcornelissen]

Summary

Originally posted by @pallymore in #1080 (comment):

I've noticed the following is also considered a side effect violation:

function SomeReactComponent() { ... }

// ❌ this is reported as a top level side effect violation
SomeReactComponent.displayName = 'MyComponent';

is this expected?

I think it's reasonable to provide an option to allow this pattern. Even though it can be quite "dangerous" (e.g. you can add a new property to an object from another module), in the described case it's pretty reasonable to want to add a property while there's not workaround to add the property at the time the object (a function in this case) is created.