25946 Mari support

- Added Alembic Cache publish to Maya secondary publish hooks
- Added Mari publish hooks and functionality to export texture channels & layers
- Fixed resizing issue in items list
- Unrecognised items returned by the scan-scene hook are now ignored - previously they would raise an exception
The Alembic cache export is intended to be a geometry cache at the moment so if they wanted to export a non-geometry alembic then the would need to update the hooks (this same check is done in scan-scene so as long as the scene hasn't changed, this will never be hit here!).