Animated blocks only use the first element within flipbook_textures.json instead of their own

The bug

The flipbook texture atlas lets you define textures in the same way as in blocks.json and terrain_texture.json, by defining a resource name in both files. However, animated blocks only use the first flipbook texture defined, instead of the ones they are assigned to.

Steps to reproduce

• Download and apply the attached packs.
• Load up a world with them and place down the two custom blocks, bug:flipbook_1 and bug:flipbook_2. Flipbook Block 1 has an animated rainbow texture, while Flipbook Block 2 has an animated grayscale texture.

→ Flipbook Block 2 does not have a grayscale texture as defined.