Add beforeDeactivated hook

[danyadev]

What problem does this feature solve?

I use :key and keep-alive tag to display chats. And in order to maintain the position of the scroll when switching between chat rooms, I need to save the scrollTop when the hook is deactivated and put it on the element when the hook is activated. But the deactivated hook is already called when the element has been removed from the DOM, so I needed a new hook - beforeDeactivated.

Seriously, this hook is needed just like the others before* hooks.

What does the proposed API look like?

Here, I think, everything is clear. Simple hook.

[dsseng]

I want to do this

[danyadev]

oops