Support Unity 6.7 content directory analysis (ContentLayout.json v3)

The schema of ContentLayout.json is changing between Unity 6.6 and 6.7 which breaks the ability to fully analyze content directory builds generated by Unity 6.7.

We need to update the support and try to maintain support for Unity 6.6 builds (the v2 schema). One approach might be to translate v2 to v3 files, and then only have support for importing the v3 data structures, this should be technically feasible because the changes only remove and reorganize data, no new data is added.

As part of this work https://github.com/Unity-Technologies/UnityDataTools/blob/main/Documentation/contentlayout.md should be reviewed to make sure it is accurate for both 6.6 and 6.7.

首先检查现有的 ContentLayout.json 导入和分析路径，并对比 issue 中描述的 Unity 6.6 v2 和 6.7 v3 schema。然后检查 Documentation/contentlayout.md 在两个版本中的准确性；完成标准是能够完整分析 6.7 内容目录构建，同时继续支持 6.6 v2 构建。