Update outdated animation documents to synchronize them with latest version Godot

[TokageItLab]

Closes #6640 Closes https://github.com/godotengine/godot/issues/72526.

Most of the problematic (outdated) topics/images were replaced. However, the AnimationTree gifs will need to be updated again after the demo project is updated.

[YuriSizov]

Images need to be converted into WebP.

[TokageItLab]

Converted images to webp for these changed in this PR.

[akien-mga]

Thanks!