Tiny splat shader refactoring

[kemchenj]

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The performance should be slightly better, and the rendering stays the same:

[kemchenj]

To extract the maximum performance, I actually think it's necessary to add a uniform matrix_model_view, which should be calculated on the CPU side in one go to reduce redundant calculations on the GPU side.

This is especially true for cases like Gaussian Splatting, where the amount of vertex computations is particularly large.

[mvaligursky]

looks good, thanks!