Update to glTF-Transform 4.0

[javagl]

glTF-Transform 4.0.0 has recently been published.

We should consider an update soon. The first pass would be to "just update the version number and see whether the compiler complains" (and then see whether the tests are still passing).

I haven't studied the change log yet. Unless there are severe, conceptual breaking changes, I wouldn't expect too much hassle here - except for the implementations of the metadata extensions. These are "closer to the guts" (internal implementation details) of glTF-Transform than the other parts of the tools, and might therefore be affected even by more subtle changes.

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One thing that has to be updated and can therefore be tracked here: In the context of upgrading CMPT to GLB, the corresponding PR derailed into one that started to cover the (huge and open) topic of "merging metadata". As part of that, some functions from glTF-Transform 4.0 have essentially been copied to an internal utility class (with notes about the source for attribution, of course!). These should be replaced by the built-in functions after the update.