Merge all the small UBOs used by the engine to save binding slots.
Each module is still responsible for filling its own data (by storing a
reference to it at construction) and this data is still private for other
modules.
The engine instance pushes the data to the GPU at the end of
`end_sync`, so only the modules that modify their data outside of the
sync functions need to manually call `Instance::push_uniform_data()`.
Pull Request: https://projects.blender.org/blender/blender/pulls/112046
e5f6c57f8c