Fix imported Java Entity models exploding when there are multiple nested groups

[JoshieGemFinder]

Problem

This pull request fixes a particularly annoying bug that would cause imported modded entity models to "explode" when there were multiple nested model groups.

This was because Blockbench would re-apply the model group transformations multiple times, causing part offsets to get way too big the further they got from the origin.

Additionally, the model would be exploded in different ways depending on the order that cubes, origin points, and children were assigned.

Example

Here's an example of what used to happen to such a model when imported from Java code (pictured model code here; viewed from the default "Isometric Right" angle):

Solution

This pull request fixes that by breaking up the import into two parts:

1. Import all of the groups / cubes relative only to themselves / their groups (i.e. ignore parent transforms for now).
2. After all groups and cubes are imported, only then apply parent transforms.

This fixes the issue with transforms being applied multiple times during an import, as they are all processed at once in the second step.

Example

Here's that same model from earlier, imported with the new code from this pull request (same model as before; viewed from the default "Isometric Right" angle):

This is what the model was originally intended to look like (and how it renders in-game), showing that the bug has been fixed.

Note

Admittedly, I haven't tested this with many models from other versions, but I do not believe it should cause any issues.