fix(geojson-layer): initialize strokeColor for LineString features (#2305) (#3338)

When loading GeoJSON data containing only LineString/MultiLineString
features, setInitialLayerConfig did not set a strokeColor, leaving it
as null. This caused the stroke color picker in the layer panel to show
a different color than what was actually rendered (which fell back to
the layer's base color).

Now LineString-only layers get explicit strokeColor initialization
matching the behavior of polygon layers, ensuring the color picker
accurately reflects the rendered line color and that user changes
to stroke color take effect immediately.

Closes #2305

Signed-off-by: pierreeurope <pierre.europe@pm.me>

Author: pierreeurope

src/layers/src/geojson-layer/geojson-layer.ts

@@ -637,6 +637,13 @@ export default class GeoJsonLayer extends Layer {
     } else if (featureTypes && featureTypes.point) {
       // set fill to true if detect point
       return this.updateLayerVisConfig({filled: true, stroked: false});
+    } else if (featureTypes && featureTypes.line) {
+      // for line features, set strokeColor so the color picker reflects the actual rendered color
+      return this.updateLayerVisConfig({
+        stroked: true,
+        filled: false,
+        strokeColor: colorMaker.next().value
+      });
     }
 
     return this;