Use cube chunks for weights in aggregations with smart weights

[schlunma]

✨ Feature Request

In weighted aggregations (Cube.collapsed, Cube.aggregated_by, etc.), it is possible to use smart weights (cubes, coordinates, cell measures, or ancillary variables), see #5084. Currently, if those weights need to be broadcasted to the cube's shape, the chunks of the resulting weights may not necessarily be aligned with those of the cube. It should be fairly straightforward to align them (see #5620).

Motivation

Aligned chunks of different arrays in a computation improves computational performance.

I'll try to implement a PR for this soon.