[Maps] Layer flashes when changing styling params

[thomasneirynck]

Kibana version:

7.10

Describe the bug:

When changing the styling (e.g. fill color) of a grid-layer using the super-fine option, the layer flashes

Steps to reproduce:

1. add cluster layer
2. set super-fine selection
3. change fill-color

-> tiles get refreshed even though only a style property has changed. this causes the layer to flash

Expected behavior:

only the style changes, not the actual source

[elasticmachine]

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