[Maps] selecting a different layer when the layer-panel is open does not change the layer-name

[thomasneirynck]

Some of the details in the layer-setting panel do not update when selecting a different layer.

to reproduce:

1. add two layers to a map
2. click on a layer in the TOC -> panel opens
3. click on another layer in the TOC -> layer-name should change in the panel (it doesn't)

[elasticmachine]

Pinging @elastic/kibana-gis