feat(2d): add animated image (animated WebP) playback support

[Tianze-Chen]

Add a layered animated-image feature: a low-level AnimatedImagePlayer, an AnimatedImage component, and a pal/image-decoder PAL with per-platform backends. The web backend uses the native WebCodecs ImageDecoder with a bundled libwebp WASM fallback; other platforms fall back to WASM.

The AnimatedImage component plays on the sibling Sprite and accepts three sources: an ImageAsset (a webp imported the default way — recommended and default), a remote URL, or a local BufferAsset. Only the field relevant to the selected sourceType is shown in the inspector.

Also register the IMAGE_DECODER system-info feature, wire the pal mapping and animated-image module in cc.config.json, add the Feature Cropping entry and i18n, and include a runtime demo under docs/examples.

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Changelog

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• changes public API, and have ensured backward compatibility with deprecated features.
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