seq<seq<'T option>> in Histogram2d,Heatmap,.. for x,y and z

[MichaelMay81]

For Heatmaps with Categorical Axis Labels (https://plotly.com/javascript/heatmaps/) we need a two dimensional list for the Z axis. Option values make life easier with missing samples. For one dimensional lists there are option variants, but sadly not for two dimensions.

[MichaelMay81]

Just realized, that I should use the heatmap and not the Histogram2d :)
But same request here.