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.

まず、既存の ContentLayout.json のインポートおよび解析パスを確認し、issue に記載された Unity 6.6 v2 と 6.7 v3 のスキーマを比較します。次に Documentation/contentlayout.md を確認し、両バージョンで正確であることを検証します。6.7 のコンテンツディレクトリのビルドを完全に解析でき、6.6 v2 のビルドのサポートが維持されれば完了です。