This mainly adds DNA level IDProp storage for system properties, their
handling in data management code, and the forward-versioning code
copying back content from system properties into 'all-in-one' single
IDProperties storage, for data types that will support both in Blender
5.0.
There is no user-facing changes expected here.
Part of #123232.
Pull Request: https://projects.blender.org/blender/blender/pulls/139257
f6a9f082e9