Coordinate maps layer dropdown not populating

[kindsun]

Kibana version:

8.x

Describe the bug:

When creating a coordinate map, the Layer dropdown under Base layer settings should minimally populate with the default roadmap, however it currently appears not to be populating at all.

Steps to reproduce:

1. Create a coordinate maps using any of the sample datasets
2. Go to Options > Base layer settings > Layers, no layers available in dropdown

[elasticmachine]

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