Consider reverting #14387 "Deprecate is_playing_animation" for 0.15

[mgi388]

#14387 deprecates is_playing_animation.

But #15962 PR merged after that prefers the is_ format following the std lib preferences (ref: #15834 (comment)). In that PR, the change was:

• Stowatch::paused -> Stopwatch::is_paused

So it seems like is_playing_animation should be undeprecated.

[cart]

I agree. is_playing_animation is more idiomatic.