Documentation should state that React preserves setState callback this context

I just recently found out that setState's callback calls with the correct this context per this line in the React source. Nowhere in the documentation is it stated that React internally calls callbacks with context. This should be made clear as many assume it doesn't, leading to unnecessary measures such as arrow functions, explicit binding, etc.

The lack of explicit documentation also creates confusion with other things that do require binding, such as traditional class methods used as event handlers.

Start with the linked ReactFiberUpdateQueue.js line and review the existing setState callback documentation. Done means the documentation explicitly states that the callback receives the correct this context and distinguishes this from class methods used as event handlers.