Fix armored elytra rendering and armor stats

[OpenBagTwo]

BCLElytraItem / FabricElytraItem does not actually inherit from Items.ELYTRA which is why this was failing.

I was worried about not having the == null check that's in the current 1.20.3 branch code, but not only does the IDE complain about it if I include it (says that itemStack is never null), but the rendering behavior works fine without it—third-person renders as expected when I un-equip my armored elytra or when I use a regular elytra or chestplate.

[OpenBagTwo]

After 7c82ecc, I confirmed that the following armor stats matched what they were on 1.20.4:

Crystalite

Item	Armor	Knockback Resist	Toughness
Helmet	3	*	1.2
Chestplate	8	*	1.2
Leggings	6	*	1.2
Boots	3	*	1.2
Elytra	6	*	0.96

Aeternium

Item	Armor	Knockback Resist	Toughness
Helmet	4	2	3.5
Chestplate	9	2	3.5
Leggings	7	2	3.5
Boots	4	2	3.5
Elytra	7	2	3.04

*These were 1.0 previously, and are zero now. I took this as an intentional nerf. If that was not the case, I'm happy to change them back to 1.

[OpenBagTwo]

@frankbauer this PR should now resolve #442 / #419

[OpenBagTwo]

Now corrects an oversight in #438 where I hadn't realized I needed to explicitly register End Veil as a tradeable enchant

[OpenBagTwo]

Now resolves #449, though @frankbauer, if you'd prefer to implement this in the datagen, I can remove that commit from this PR.

[oscarmag2]

How do i get these fixes?

[tonitch]

I don't know a lot about how this works but this doesn't seem to allow the crystalite elytra to be enchanted with unbreaking and mending. I could enchant with prot 4 and thorns 3 though

[OpenBagTwo]

Just pushed three more fixes around Crystalite armor.

@tonitch Just using an enchanting table, right? I've been able to add enchantments with an anvil, but I can't figure out what tag I'm missing to allow them to get Unbreaking.