Drop the addition of `XModuleMixin` for the `xblocks-contrib` xblocks [here](https://github.com/openedx/openedx-platform/blob/2637cc6b0f8a5e094bb1f59b2b640fb59959b226/lms/envs/common.py#L1075) It's the R&D story to find the implementing and testing way to drop the addition of XModuleMixin for the xblocks-contrib xblocks