Moved the requirement for memory visibility of a Reducers internal state

... (maintenance)... to the framework by piggybacking it to an internal field

fixed #3866 
We need to move it out of the public API one way or another :) Don't uglify your API due to an implementation issue. So we should get rid of the methods.

There are other solutions. I'm 110% fine relying on the memory visibility effects of another structure as long as it is documented.