Capture React.startTransition errors and pass to reportError (#28111)

To make React.startTransition more consistent with the hook form of
startTransition, we capture errors thrown by the scope function and pass
them to the global reportError function. (This is also what we do as a
default for onRecoverableError.)

This is a breaking change because it means that errors inside of
startTransition will no longer bubble up to the caller. You can still
catch the error by putting a try/catch block inside of the scope
function itself.

We do the same for async actions to prevent "unhandled promise
rejection" warnings.

The motivation is to avoid a refactor hazard when changing from a sync
to an async action, or from useTransition to startTransition.