Ease passing data from before to after hooks

[dk1a]

I need both the previous and the current value of an arbitrary table in a hook

• Then I either form the updated value in onBefore using hook arguments, which can get very complex with splices and all the different hooks
• Or I pass the previous value from onBefore to onAfter using some storage stack, which can get gas intensive (and possibly leaky?)

I think having onBefore return a memory blob, and onAfter accept it as an argument would significantly improve this issue.
It's simple enough and I can PR it if you agree with the idea

On the other hand it's not a significant issue, especially if you think this solution would cause more problems

Perhaps this could apply to system hook too, but I don't have a use-case in mind