Lookup conversion helper functions

[alex-s-gardner]

I find myself needing the utility of these three lookup helper functions contained in GeoMakie and I'm wondering if it would make sense to bring these over to DD:

DimensionalData.jl/ext/DimensionalDataMakie.jl

Lines 631 to 660 in 79b2f87

	function _lookup_to_vector(l)
	if isintervals(l)
	bs = intervalbounds(l)
	x = first.(bs)
	push!(x, last(last(bs)))
	else # ispoints(l)
	collect(parent(l))
	end
	end
	function _lookup_to_vertex_vector(l)
	if isintervals(l)
	return parent(DD.shiftlocus(DD.Center(), l))
	else # ispoints(l)
	return collect(parent(l))
	end
	end
	function _lookup_to_interval(l)
	# TODO: warn or error if not regular sampling.
	# Maybe use Preferences.jl to determine if we should error or warn.
	l1 = if isnolookup(l)
	Sampled(parent(l); order=ForwardOrdered(), sampling=Intervals(Center()), span=Regular(1))
	elseif ispoints(l)
	set(l, Intervals()) # this sets the intervals to be `Intervals(Center())` by default. Same as heatmap behaviour.
	else # isintervals(l)
	l
	end
	return IntervalSets.Interval(bounds(l1)...)
	end

[rafaqz]

These are very Makie specific things, the vector length is length(lookup) + 1 because Makie wants that. And the vertex is because Makie specifically wants center points.

I don't think we can export these as general use functions.

[asinghvi17]

I would say that edgevector on at least Regular and Irregular lookups would be valuable for histograms etc?

[rafaqz]

Maybe, I'm not sure it's worth the extra function when we have intervalbounds already