[New Feature] Decouple terrain type animation looping from Tiberium-spawning

[Crimsonum]

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Description

Terrain types can be animated using IsAnimated and related keys, but the animation will loop only if the type also has SpawnsTiberium=yes defined. If not, the terrain type will animate through all the frames and become invisible. This means that only Tiberium-spawning terrain types can be properly animated.

Proposed Code (optional)

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Additional Context

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