fix broadcasted assignment for scalar cartesian indexing (#35926)
* fix broadcast for scalar cartesian indexing
When broadcasting left-hand side indexing is turned into a dotview.
For scalar indexing this should be equivalent to a `getindex`, but up
until this patch the `CartesianIndex` would not be treated as such.
This fixes e.g. broadcasting like `a[CartesianIndex(1)] .= 1` for a nested
array `a`.
* Also extend to `AbstractCartesianIndex`es
Co-authored-by: Matt Bauman <mbauman@gmail.com>
