Add "previousValue" parameter to @PostUpdate @PreUpdate handler

[trajano]

I am pretty sure this can't be done easily because we only have references and can't simply just "copy" the previous value first for @PreUpdate and @postupdate

That is saying something like

@PreUpdate
void aboutToUpdate(Entity out, Entity in) {}

@PostUpdate
void updated(Entity out, Entity in) {}

The idea I had that if a second parameter is provided namely in then it's the object that was about to be updated but detached. The thing is if it was still pointing to the same values as the out entity they'd be the same values.

So for someone to work around that in may have a transient variable containing the older values which will be dropped off the out parameter. Then they can do some manipulations.

Anyway just a random idea.