Use color tag as fill color if it exists

[biamalveiro]

Goal

When a map feature includes a "colour" tag, we interpret it and use it as the fill color for the feature.

Description.

For the layers landuse-nature, landuse-forest , landuse-urban, landuse-greenspaces, road, building, we add the following case condition on the map style spec:

["case", ["has", "colour"],["get", "colour"], ["literal",${default color}]]