Add promotion rules for `CategoricalArray`s and views of `CategoricalArray`s

[nalimilan]

On Julia 1.9, we get this (see #385):

julia> [categorical(1:2), view(categorical(1:2), :)]
2-element Vector{Vector{CategoricalValue{Int64, UInt32}}}:
 [1, 2]
 [1, 2]