Blender Git Loki

Fix T61935: load camera transforms from Alembic files written by Meshroom

Meshroom writes two hierarchies to Alembic, one rooted at
`/mvgRoot/mvgCameras` and the other at `/mvgRoot/mvgCamerasUndefined`.
These paths have no schema definition, and thus are ignored by Blender.
The cameras themselves have those schemaless paths as parent, and have
their transforms marked as "inherited", e.g. relative to their parent.
As these cameras have no valid parent, there is no Blender object to use
to convert their local matrices to world matrices, and Blender just
decided to reset them to the unit matrix.

Now "inherited" transforms without a parent in Blender are interpreted
as world transforms. Reparenting those objects to a Blender object will
re-interpret the transforms as local to the parent again.