Better choices for fluid side textures

[muzikbike]

Request Description

This may be out of scope as a feature request as well as a change to vanilla behaviour which could also affect mods, however since #2471 is accepted as a valid candidate for fixing I suppose this may be worth bringing up as well since it touches on much the same area of code.

Currently, vanilla's application of textures to the sides of fluids is something I find strange. For source blocks, the downwards flowing texture is used, even if the fluid in question isn't actually flowing downwards. For water, if it's against certain solid blocks, the downwards flowing texture is replaced with a solid color translucent texture, which is easier on the eyes, but still feels like a suboptimal solution.

Bedrock Edition, in my opinion, does things much better: the sides of source blocks (provided they aren't flowing) is simply the still texture for that fluid. I think Sodium should replicate this behaviour.

Fluids that are flowing downwards would still use the downwards flowing texture, of course:

Another issue is the side texture of horizontally-flowing fluids: it, too, appears to be flowing downwards. It would make much more sense for the texture to be instead rotated so that it's pointing in the flow direction, either left or right.

Again, no idea if this is wildly out of scope even if it is close to a separate, valid issue, so tell me if I should or shouldn't open more tickets like this one.