Remake arm rendering to remove the elbow joint + other limb-related ideas (such as tracker support, FPM fix)

[Truemudkip]

This is a suggestion if you couldn't tell, it's not showing me if there's a label I can give this issue so it's marked as enhancement.

I've thought about some ideas that i think could help the mod fit in better with Minecraft itself, and other mods (mainly First-Person Model). Take note that if this issue/suggestion has a theory on implementation, it's probably wrong, as I don't know coding, but I have a rudimentary ide on how it works.

1. Reworked arm rendering: Arms should be rendered as one block that's the entire arm, instead of the invisible elbow cut-off we have now (think a Minecraft trailer where the various player representations still flail their arms around, but they stay one solid block), and armor bits that show up on arms (example: the shoulder pieces from vanilla chestplates, the Create Mod Netherite Backtank arms) should appear on the player's arms from first person (this could also help fix 3., and help with support for mods like Create's Netherite Backtank, that completely covers the arm in armor).

How I think this could be implemented: The arm model, from the outside, now bends in the direction of the controller, simply being a line from point A (simulated shoulder) to point B (controller). The length difference can either be solved by giving the arm a small area around the shoulder to freely extend, and to compress its model when the controller moves closer to the shoulder that the arm model's length + the shoulder tether area allow (the shoulder tether area may help with unnecessary compression of the arm). Another way to implement this without compression is to push back the entire arm, but that solution might look a bit goofy (e. g. putting your controllers on your chest IRL may make the ends of the arms stick out weirdly).

2. Tracker support (may require OpenXR support to be available for Vivecraft but I don't know): Add 3-point tracking setup support to Vivecraft (a 3-point setup consists of a tracker on the top of each foot to track the legs and a tracker at the base of the spine to track the hips). Implementing 1. may help with this by reusing code for the arm rendering for the legs.

How I think this could be implemented: No idea how this would be coded, in my opinion the best way to add it would be code reusing from 1./arm rendering for outside viewers.

3. Fix First-Person Model chestplate issue: First-Person Model is currently broken, not showing the chestplate, if one is eqquiped.

How I think this could be implemented: This issue can most likely be fixed by solving the chestplate arm-based pieces, as i think what Vivecraft currently does is opt not to render the chestplate altogether to avoid showing the shoulder pieces.

[fayer3]

1. has issues when you move you are closer, the split is to allow small and big distances
2. fbt is planned, but not a priority right now

[fayer3]

also, rendering the armor on the arm will block the gui, which is not ideal