fire componentWillDisappear event before starting transition animation

[flexsurfer]

🚀 Feature

it would be useful to know in JS when transition animation is started so some computation may be done in that time, and the previous screen will be opened updated

Implementation

fire componentWillDisappear before starting transition animation

EDITED:
found the comment #4793 (comment)

but I think these events still will be useful

[erennyuksell]

i need this definitely