Show data labels for all levels in Treemap series. about highcharts

[TorsteinHonsi]

Internal note

This feature has been on our radar since we first implemented treemaps. In order to keep the node areas correct, we need to go in on the algorithm level and reserve a fixed space for the data labels. We can assume that the height of each data label is fixed. The width would be the same as the leaf or group. Then the rest of the layout would take this reserved area into consideration.

At the same time, it may make sense to consider padding or spacing between the nodes, which will make a nested layout more readable. This also complicates the computation of the areas, as each leaf not only contributes with its own area, but also that of the padding + heading:

[TorsteinHonsi]

Duplicate of #17243