Remove group.id property

[lilleyse]

Removes the group.id property so the groups are consistent with other metadata entities. Metadata entities such as tilesets, tiles, contents, and groups should use the ID semantic.

There was some discussion about this in #648 (review).

[javagl]

Related to the broader question of "id vs. index" : One could make a case that

• things that are values in a dictionary should not have an "id"
• things that are entries in an array should have an "id"

(The reason being related to the question of what the ID is used for. If it's used for identifying things, then it has many constraints in terms of uniqueness that do not apply directly when there already are "ids", namely, the dictionary keys)

But in general, that change is fine for me, at least to have consistency.

Now becoming more relevant: CesiumGS/cesium#10223

(Also, I'll have to update the samples that needed ID to circumvent this issue)

[lilleyse]

Now becoming more relevant: CesiumGS/cesium#10223

Yes, thanks for the reminder. @j9liu could you look at that?

[lilleyse]

(Also, I'll have to update the samples that needed ID to circumvent this issue)

Does that just include https://github.com/CesiumGS/3d-tiles-samples/tree/main/1.1/MetadataGranularities?

[javagl]

Does that just include https://github.com/CesiumGS/3d-tiles-samples/tree/main/1.1/MetadataGranularities?

Yes, this seemed to be the only model that defined groups for now. The PR is at CesiumGS/3d-tiles-samples#46