[Ghostipedia]

What

This is a cherry-pick and then adaptation of all cumulative render fixes/changes that culminated in #5370 and then #5376
See PR description, it's a long one, but the goal of this PR was to backport it.

Implementation Details

This was done by first cherrypicking the relevant PRs down to 1.20, checking what was there, different, was strictly a bad cherrypick, etc. and then a few commits focused on removal/adaption/migration.

FaceLayer has been properly implemented as well, works as expected

AI Usage

Yes, Codex 6.1 Sol on medium
Used to compare the render backends of 1.20 and 1.21 and note what should/shouldn't be kept. I'm pretty familiar with these as well so this was mostly used for migration/automation/verification.

Outcome

Both 1.20 and 1.21 have visually consistent render behaviors. Pipes still have some rendering issues, but I will be fixing that on 1.20 and 1.21 in a seperate PR, as I do not want to overscope this PR to start fixing every small issue I find on 1.20 compared to 1.20

How Was This Tested

Eyeballs, lots of eyeballs, renderdoc captures, and generally verifying the same way the original PR was handled

Potential Compatibility Issues

Uh, as stated with the last one

The sodium and embeddium integration only targets internal chunk renderer consumers. They're pretty scoped to the points those things allocate or handle.

Compatible Sodium/Embeddium versions are restricted via our mods dependency ranges, meaning we can actively be away of if/when changes are needed, and the extent of them. because these entry points are so scoped, it'll be the best compromise. (If i could have done this 100% without mixins, i would have liked to, but alas MC, Neoforge, and literally everyone else seem to not want to do a genuine extension to Renderlayers)

Addon models without gtceu:face_layer continue to render using the fallback layer, addons can just opt in by updating relevant datagen / model jsons. Documentation will be provided shortly in a future PR after one last PR handles some small other visual edgecases I'd like to address that also need docwork for this whole system.

FaceLayer docs will not be included with this PR until the pipe related fixes are done for 1.20 and 1.21, as they may need adaptations that would constantly block this PR. hence why they are still not done.

[Ghostipedia]

Will be working on this over the next few days/weeks/whenever I have the time.
This does not compile.
Tests will be very mad.
Things will look, grossly out of place for now.
This literally was just the cherrypick and the conflict fixing.
😫