Support obtaining the curve of AnimatableCurve

## What problem does this solve or what need does it fill?

Allow modification of known animation curves, random or targeted adjustments to animation curves.

## What solution would you like?

```
impl Debug for AnimatableCurve
where
C: Debug,
{
fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
f.debug_struct("AnimatableCurve")
**.field("curve", &self.curve)**
.finish()
}
}
```

I have noticed that dyn AnimableCurve supports printing on debug traits that have already been implemented, so I think it is possible to allow C generics to return data when implementing a certain trait.

So only when the C generic supports a certain trait, will it return the actual data of AnimableCurve.

Meanwhile, this trait supports converting data, just like converting any trait to an actual type.

## What alternative(s) have you considered?

Not.

## Additional context

I haven't found any known AnimatableCurve to obtain actual curve data, please let me know if there is.