Multires Modifier: Add interpolation methods for vertex weights and groups

Currently, adding any kind of deformation or rig that utilizes vertex weights will create artifacts on a mesh with multiple resolutions like so:

^ Notice the bands of light that happen on the low resolution mesh's polygon boundaries. This is a simple mesh with multires enabled that is followed by an armature modifier for posing and animation needs.

This is non-ideal and I imagine this makes the multires modifier a no-go for most production needs.

My guess would be that vertex weights are not interpolated from the low poly, but the logic behind why this isn't presumed in the subdivision process isn't clear to me. I know, for example, that I could apply the high resolution details and then proceed to transfer over all weights using a data-transfer modifier.

So I propose that there'd be a simple weight-transference setting that simply uses face-interpolated weight values derived from the low resolution mesh. So each subdivision would have interpolated weights by default, which would then be disabled for advance users who might not want this in the default behaviour (It's unclear why this would be necessary, but it must have been a decision someone made along the way.)