Consider a command to change the metallic value of GLBs in B3DM

[javagl]

Apparently, FME creates 3D Tiles tilesets where the metallicFactor in the glTF assets in B3DMs is set to 1.0 (the default value). In an ideal world, we'd open an issue in their repo, and this would be fixed in the next release. But in reality, poeple seem to stumble over that, because it shows up as textures being "too dark" and surfaces being "too shiny", e.g.

• https://community.cesium.com/t/3d-tiles-get-very-dark-textures/26323
• https://community.cesium.com/t/change-shiny-surface-quality/26679
• ...

The first thread ended with a snippet that is based on a certain commit state of the 3D Tiles tools, using and internal API, and that may break at any point in time. It was just intended as a workaround that the user had with one particular tileset.

If this comes up more frequently, we could consider offering a more stable (maybe even command-line) functionality for modifying the metallicFactor in all tile contents of a tileset.