Update code-editor for animation

[nighca]

• Update code-editor for animation, update Animation support #543

  1. Add animation-related tools, e.g. step, & update description for existed tools
  2. Add animation definitions of current sprite in Variable tools
  3. Exclude costume-index related tools or usages

• Fix costume add problem introduced in Costume pre-processing: split-sprite-sheet #614

[nighca]

这里修复之前 #614 引入的 bug：添加 costume 时选择一张图片会得到两个 costume

cancelMethod 也会触发 updateCostumes，因此会触发几乎同时的两次 updateCostumes 调用（对应相同的参数）

而 updateCostumes 里边

1. 清空 selectedCostumes
2. 向 selectedCostumes 中添加新的 costumes

两个动作之间间隔了 await Promise.all() 的过程；因此两次 updateCostumes 调用对应地清空了两次 selectedCostumes，然后又向 selectedCostumes 中添加了两次新的 costumes

最终导致输入一个文件，而 selectedCostumes 中保存了两个 costume

[qiniu-ci]

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