Blender Git Loki

Fix (unreported) copying liboverride of mesh breaks overrides of shape keys.

Our beloved shapekeys are 'virtual' overrides, they need special
snowflake treatment here as well.

They do not have any override data, from override perspective they are
considered as mere sub-data from their owning ID (mesh, lattice, etc.).
Therefore, we should not copy override data from them, but instead
properly flag those new IDs as `LIB_EMBEDDED_DATA_LIB_OVERRIDE`.

Found while investigating T84373.