Fix hidden slider fade

[frankZZzzzzzzzz]

Fixes issue #37532
Since slider body should start fading after head disappears and slider body fades in at same time as head, offset body fade out start by head fade out duration and decrease long duration by the same amount

First ever open-source contribution, yay (I HAVE SAVED HD)

Comparison.mov

[peppy]

Comparison video looks correct. Are you able to also compare with default skin just to make sure it's not regressing anything? Inline comment explaining with this adjustment is required may also be good.

[WitherFlower]

It would be useful to make the comparison with the "snaking out sliders" setting unchecked in lazer, for the sake of consistency with the stable visuals

[frankZZzzzzzzzz]

I think the 3rd slider shows the difference of when the body starts fading the best while the 2nd slider shows the difference in fading out best.

Also of note: It seems that on Stable the slider body finishes fading in when the slider head disappears instead of fading in with the head. Maybe want to change that? (Although I think that WOULD be too much of a stretch to make lazer like stable)

After is slightly ahead than Stable and Before (<1 frame at 120fps -> 50% speed)

Comparedefault.mp4