Support classified color palettes in the Cesium map

[robyngit]

Colors for 3D tileset layers are set in the Cesium config using the colorPalette property.

categorical colorPalette example

"colorPalette": {
  "paletteType": "categorical",
  "property": "Type",
  "label": "Zone type",
  "colors": [
    {
      "value": "Climate-driven",
      "color": "#FF3720"
    },
    {
      "value": "Climate-driven/ecosystem-modified",
      "color": "#0370FE"
    },
    {
      "value": "Climate-driven/ecosystem protected",
      "color": "#BFD1FF"
    },
    {
      "value": "Ecosystem-driven",
      "color": "#4DE603"
    },
    {
      "value": "Ecosystem-protected",
      "color": "#267301"
    },
    {
      "value": null,
      "color": "#ffffff"
    }
  ]
}

In the example above, paletteType is set to categorical. This type means that each feature's property must exactly match the the value for the feature to be shaded with the corresponding color. Only categorical and continuous palettes (#1952) are supported so far.

This issue encompasses adding support for classified color palettes. - classified color palettes are for numeric properties like area and height, but the palette is discrete instead of a continuous gradient. That means that the configured values would be interpreted as maximums, and any values less than the given value would be "binned" into a discrete color category. This differs from the categorical palette in that the features' property values do not need to exactly match the configured color value, e.g.:

Notes:

• This issue is about rendering the features in the correct color when there is a continuous or classified color palette configured in the cesium config. Building the UI to allow users to change the color palette live in the map is covered by Support changing the color of features in a data layer #1768.
• When this type of palettes is supported, make sure to also support them in the LegendView (see Add a preview/thumbnail for each layer in the layer list in the cesium map #1886 and Show a legend for data layers that require one in the Cesium View #1784)
• This issue was original part of issue Support continuous and classified color palettes in the cesium map #1888