Add a param generic to Animator to allow multiple tweens over the same component

[meepleek]

I love using this crate, but not being tween parts of the same component at different times (I guess it might be possible to recreate a Tracks tweenable?) can be quite cumbersome (I'm looking at you, Transform). Enter marker components to have different types of animators based on the marker.

    commands.spawn((
        Sprite {
            color: RED.into(),
            custom_size: Some(Vec2::splat(size)),
            ..default()
        },
        Animator::new(translation_tween).with_marker::<TransformTranslation>(),
        Animator::new(scale_tween).with_marker::<TransformScale>(),
        Animator::new(rotation_tween).with_marker::<TransformRotation>(),
    ));

There's a bunch of stuff missing, hence the draft state. Lemme know if you think it would be of value.

Things to do to move this out of draft state

• go-ahead from @djeedai
• AssetAnimator
• docs
• tests
• better example to show how this might be useful compared to a Tracks tweenable
• dupe the animator systems to avoid introducing breaking changes?

[meepleek]

Closing as stale