Implement sprite animations

[s-puig]

WIP. Posting this to see if this is wanted or should be a third-party crate.

Objective

• Implement sprite animation

Solution

• Determines the sprite index based on time since animation start at the end of every frame.

Testing

Unit tested the player. They are of questionable code quality but should be accurate.
Still missing quite a few though

---

Showcase

SpriteClip basics

let clip = SpriteClip {
        // Clip frames also accepts Handle<Image> for people who don't want to deal with atlases
        clip: ClipFrames::from([0, 1, 2, 3, 4, 5, 6]),
        speed: 1.0,
        // number of frames per second
        fps: 1,
        // Also has Repeat(usize)
        clip_loop: ClipLoopMode::Infinite,
    };

// Clip is an asset so you can change the behaviour of an animation for all entities and load them via asset_server
let clip = asset_server.add(clip);
// Clips can easily be overwritten without affecting the underlying asset
let overwritten_clip = clip.clone().overwrite().backward().fps(2));

SpriteAnimationPlayer basics

// It uses SpriteAnimationPlayer component
let mut player = SpriteAnimationPlayer::default(); //all fields are public but it might be more convenient to use new or default
// and are added like any other component
commands.spawn((
        SpriteBundle,
        TextureAtlas,
        player,
    ));
// Players are also assets
let player_asset = asset_server.add(player);
// and can be added to entities allowing synced animations (useful for stuff like trees and water)
commands.spawn((
        SpriteBundle,
        TextureAtlas,
        player_handle,
    ));
// Player has the expected methods
player.play(clip.clone().overwrite().backward().fps(2));
player.stop();
player.resume();
player.restart();
// Transitions can be configured (WIP)
player.play_with_transition(clip, TransitionMode::AnimationEnd);

[alice-i-cecile]

Strong yes please to upstreaming this. Very overdue.

[github-actions]

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