[FEATURE] - Replace Voxelizer and LayerRegridder logic with xugrid's Regridder logic

Currently the Regridder for 2D grids can already be replaced with xugrid's. Right now we still throw a DeprecationWarning, but we will eventually remove these classes. The LayerRegridder and Voxelizer, however, still have no full replacement in xugrid.

As mentioned earlier, there is backend logic to eventually replace the Voxelizer and LayerRegridder, but it hasn't been exposed (and probably not well tested):

The most important thing is that the xugrid one is missing the Voxelizer and LayerRegridder, essentially.

This requires top and bottom data, or bounds on a z coordinate. I've implemented the logic for computing the weights: https://github.com/Deltares/xugrid/blob/fc0bdcb0eaeff62887f1e62fadd61957629dff61/xugrid/regrid/overlap_1d.py#L158

But it's not exposed yet here (class exists: https://github.com/Deltares/xugrid/blob/fc0bdcb0eaeff62887f1e62fadd61957629dff61/xugrid/regrid/structured.py#L736)

Originally posted by @Huite in #1372

Tasks are:

• Expose StructuredGrid3d and ExplicitStructuredGrid3d classes in xugrid and finish any TODOs there
• Test whether these new classes produce similar results as the original LayerRegridder and Voxelizer
• Forward calls from Voxelizer to StructuredGrid3d and from LayerRegridder to ExplicitStructuredGrid3d

Start with xugrid/regrid/overlap_1d.py and xugrid/regrid/structured.py, focusing on the existing StructuredGrid3d and ExplicitStructuredGrid3d classes and their TODOs. Expose those classes in xugrid, compare their results with the existing LayerRegridder and Voxelizer, then forward each existing class to its corresponding xugrid implementation.