Updates, features, and refactoring for Modular PBR Shaders (redo PR)

[yaRnMcDonuts]

A big PR that makes many minor changes to the new modular PBR system so it can work with PBRTerrains and any other potential forks.

Since no bugs were reported in the last alpha version, I've now replaced the main PBRLighting.j3md shader with this new modular version.

I'm still adding some small things to this PR, and still need to upload the new modular PBR terrain files, so there will probably be more changes to this PR soon, but feel free to review in the meantime.

I also plan to make another PR with some more minor improvements to further modularize the PBRSurface struct (and add some other similar structs) later on in 3.8 beta after collecting more feedback, so I'll be merging this PR very soon, likely before it gets full review. But I will ensure all feedback regarding the new Modular shader system will be addressed before 3.8 reaches stable.

[capdevon]

Hi @yaRnMcDonuts ,
Could you please follow @stephengold's practice of leaving a comment before merging code? Something like, "If no revisions are requested, I'll proceed with merging in 48 (or 72) hours." This is really helpful for community engagement and feedback. Thanks!

[yaRnMcDonuts]

I hope it does not seem like I rushed this to avoid community engagement or feedback. That is not my intention, and I apologize if I did not make it clear in my reasoning for why I planned to merge this before in-depth review.

To elaborate on this:

so I'll be merging this PR very soon, likely before it gets full review. But I will ensure all feedback regarding the new Modular shader system will be addressed before 3.8 reaches stable.

I meant to imply that some aspects of this PR were urgent and this PR is mostly changes that were necessary to fix crashes with the modular PBR shader that popped up while I was adapting it to work with PBR terrain, and I didn't want a full in-depth review to slow down an urgent bug fix, especially since the API is still in flux and I'm still actively seeking feedback with plans to make more changes up until 3.8 is in stable

I tried to split some stuff into a seperate PR that is currently open (#2353), so that this PR would contain mostly the stuff needed for the bug fixes, however due to the dependent nature of this whole new system, it was hard to split things up so I apologize if it ended up with this PR including some things that should've been in the other PR that is still open.

But I would still appreciate hearing your review on anything in this PR, and as mentioned, I will certainly address it in one of many upcoming PRs I'll be making regarding modular PR during this release cycle.