[Maps] Improve icons for all layer types

[thomasneirynck]

Describe the feature:

Enhance all icons, similar to the ES-sources and the Solution layers. This issue was raised here: #70266 (comment)

Describe a specific use case for the feature:

• EMS Boundaries

These are all boundary-layers, and most often used for choropleth-mapping. THe difference with the "choropleth"-layer, is that no styling is applied and no data is joined to it (yet!).

So maybe something along the lines of the choropleth-icon, but without the styling (?)

• EMS Basemaps

These are pre-styled "background"-layers for the entire world ("dark theme", "desaturated theme", etc...). They are not interactive. Maybe something like a little world-map?

• Configured GeoJson

These are similar to ES-documents layer (points, lines or polygons), but configured in the .yml, coming from an outside service. tbh. the Kibana-logo works pretty decently. This layer-type will likely be deprecated too in 8.0 (#81704), so I'm not sure if we need to do an effort here.

• Tile Map Service

This is a 3rd party tile-map service. These are raster images. Similar purpose as the EMS Basemaps, but from an external provider.

• Web Map Service

This is a 3rd party WMS-map service. From an external provider. These are raster images. Usually, the data is more dynamic (e.g. weather patterns), or have a more local scope (e.g. just for particular country/area, and not worldwide).

• Vector tiles

This is for 3rd party vector-tile service. Data is similar as the "Documents" layer (lines, point, polygons), but delivered in tiles. Maybe something like the "documents"-icon, but "cut up" in a little grid?

[elasticmachine]

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

[elizabetdev]

@thomasneirynck and @kmartastic,

Here are the new icons. I'm using the same icon for both EMS Basemaps and Tile Map Service.

The Configured GeoJson (will likely be deprecated) is the same as the Documents layer.

Let me know if you want to make any changes. I can create then a PR and add both light and dark icons.