[Maps] layer style editor is empty for EMS boundaries layer

[nreese]

Steps to view problem:

1. Create a new map
2. add "EMS Boundaries" layer, select any layer and click "Add layer"
3. Notice that "Layer Style" editor is empty

The style editor should look like the following (screen shot from 7.9)

This is a regression caused by #81525

[elasticmachine]

Pinging @elastic/kibana-gis (Team:Geo)