Dynamically populate filter values from data for fully loaded vector layers in Cesium maps

[robyngit]

We now have an initial UI for filtering map layers by categorical properties in Cesium maps. This UI uses the allValues property in the map config to populate the dropdown with available filter options. This approach is essential for large datasets that are loaded in pieces, such as Cesium 3D tiles, because the browser cannot determine all possible values without loading the entire dataset.

However, for fully loaded vector data like GeoJSON, the browser already has access to the complete dataset before rendering. In these cases, it would be helpful to populate the list of possible values dynamically from the data itself.

For this first enhancement, we should continue relying on the configuration to define which properties are filterable and what type of UI should be rendered. This update would focus only on dynamically filling in the allValues list using the actual data.