Support `$bumpframe` animated normal

[kristiker]

I think animation parameters in complex and others work on the whole material (so all the maps). S1import currently only supports $frame (albedo).

https://github.com/kristiker/source1import/blob/43d1009e86298599f5cef67dcb6bb2d75d56200a/utils/dev/.todo.txt#L52-L63