[Proposal] Compound Animations

Compound Animations

* [x] Proposed
* [ ] Prototype: Not Started
* [ ] Implementation: Not Started
* [ ] iOS Support
* [ ] Android Support
* [ ] macOS Support
* [ ] Windows Support
* [ ] Unit Tests: Not Started
* [ ] Sample: Not Started
* [ ] Documentation: Not Started

## Summary
[summary]: #summary

A comprehensive set of complex animations based on https://animate.style

## Motivation
[motivation]: #motivation

To provide a feature rich set of animations that users can just use.

## Detailed Design
[design]: #detailed-design

The implementation will extend the existing `AnimationBehavior` and `AnimationBase` functionality in order to reduce any additional API footprint increase.

### CompoundAnimationBase.shared.cs

```csharp
public abstract class CompoundAnimationBase : AnimationBase
{
public static readonly BindableProperty IsRepeatedProperty;

public bool IsRepeated { get; set; }

// Extension from AnimationBase
public override Task Animate(View? view);

public Task Animate(CancellationToken? cancellationToken, params View[]? views);

protected abstract Animation CreateAnimation(params View[] views);
}
```

### RubberBandAnimation.shared.cs

```csharp
public class RubberBandAnimation : CompoundAnimationBase
{
protected override Animation CreateAnimation(params View[] views);
}
```

### TadaAnimation.shared.cs

```csharp
public class TadaAnimation : CompoundAnimationBase
{
protected override Animation CreateAnimation(params View[] views);
}
```

## Usage Syntax
[usage]: #usage-syntax

### XAML Usage

```xml

```

### C# Usage

```csharp
var cancelAnimationTokenSource = new CancellationTokenSource();

var animation = RubberBandAnimation
{
Easing = Easing.Linear,
Duration = 100
};

await animation.Animate(cancelAnimationTokenSource.Token, myView, myView2);
```

## Drawbacks
[drawbacks]: #drawbacks

## Alternatives
[alternatives]: #alternatives

## Unresolved Questions
[unresolved]: #unresolved-questions

**I have left this only covering publicly exposed parts of the toolkit. Is this fine?**

**Dependent on #35**