Take glTF up axis into account during upgrade

[javagl]

Addresses #165

What this currently does:

• It checks for the presence of the tileset.asset.gltfUpAxis
• If it is found, then it is removed from the tileset JSON, and passed on the the tile content upgrades
• Until now, this is only used for the conversion of B3DM with glTF 1.0 into glTF 2.0 (when upgrading to 1.1)

It could be desirable to also use this for the upgrade to 1.0: The gltfUpAxis is a "legacy" feature that should not be part of a tileset that has been upgraded to 1.0. And this might be doable with reasonable effort.

What I'm more scared of is that the gltfUpAxis also (likely) will affect the I3DM upgrade. The coordinate system conversions for I3DM had been a hassle. The coordinate system conversions for the gltfUpAxis are a hassle. Combining this will be hassle², with the caveat that this involves generating that "legacy" data in the first place...

The current test data (which is not yet checked in, and might still change) is here:

upAxisHandling 2025-01-08.zip

It focusses on the B3DM case (with and without an RTC_CENTER in the B3DM), and makes sure that the visual appearance of the output is still the same as the input in CesiumJS (Sandcastle and output are included)

This is supposed to eventually become a test data set for the specs, using the "golden" comparison approach.