Remove TransformCurve (#15598)

# Objective

It is somewhat unlikely we will actually be able to support
`TransformCurve` (introduced in #15434) after the `AnimationGraph`
evaluation order changes in the immediate future. This is because
correctly blending overlapping animation properties is nontrivial, and
`Transform` overlaps with all of its own fields. We could still
potentially create something like this in the future, but it's likely to
require significant design and implementation work. By way of contrast,
the single-property wrappers `TranslationCurve`, `ScaleCurve`, and
`RotationCurve` should work perfectly fine, since they are
non-overlapping.

In this version release, creating `TransformCurve` in userspace is also
quite easy if desired (see the deletions from this PR).

## Solution

Delete `TransformCurve`. 

## Migration Guide

There is no released version that contains this, but we should make sure
that `TransformCurve` is excluded from the release notes for #15434 if
we merge this pull request.

crates/bevy_animation/src/animation_curves.rs

@@ -65,7 +65,6 @@
 //! - [`TranslationCurve`], which uses `Vec3` output to animate [`Transform::translation`]
 //! - [`RotationCurve`], which uses `Quat` output to animate [`Transform::rotation`]
 //! - [`ScaleCurve`], which uses `Vec3` output to animate [`Transform::scale`]
-//! - [`TransformCurve`], which uses `Transform` output to animate the entire `Transform`
 //!
 //! ## Animatable properties
 //!
@@ -370,45 +369,6 @@ where
  }
 }
 
-/// This type allows a [curve] valued in `Transform` to become an [`AnimationCurve`] that animates
-/// a transform.
-///
-/// This exists primarily as a convenience to animate entities using the entire transform at once
-/// instead of splitting it into pieces and animating each part (translation, rotation, scale).
-///
-/// [curve]: Curve
-#[derive(Debug, Clone, Reflect, FromReflect)]
-#[reflect(from_reflect = false)]
-pub struct TransformCurve<C>(pub C);
-
-impl<C> AnimationCurve for TransformCurve<C>
-where
- C: AnimationCompatibleCurve<Transform>,
-{
- fn clone_value(&self) -> Box<dyn AnimationCurve> {
- Box::new(self.clone())
- }
-
- fn domain(&self) -> Interval {
- self.0.domain()
- }
-
- fn apply<'a>(
- &self,
- t: f32,
- transform: Option<Mut<'a, Transform>>,
- _entity: AnimationEntityMut<'a>,
- weight: f32,
- ) -> Result<(), AnimationEvaluationError> {
- let mut component = transform.ok_or_else(|| {
- AnimationEvaluationError::ComponentNotPresent(TypeId::of::<Transform>())
- })?;
- let new_value = self.0.sample_clamped(t);
- *component = <Transform as Animatable>::interpolate(&component, &new_value, weight);
- Ok(())
- }
-}
-
 /// This type allows an [`IterableCurve`] valued in `f32` to be used as an [`AnimationCurve`]
 /// that animates [morph weights].
 ///