Define layer ID in Tileset YAML not in Layer YAML

[lukasmartinelli]

The ID of the layer should be defined in the tileset not in the layer YAML.
This means you can pull in the layers as you want and still give them a custom name.

So not like this.

tileset:
  layers:
    - layers/boundary/boundary.yaml
    - layers/highway/highway.yaml
    - layers/highway_name/highway_name.yaml
    - layers/building/building.yaml
    - layers/housenumber/housenumber.yaml
    - layers/place/place.yaml

More like this.

tileset:
  layers:
    boundary: layers/boundary/boundary.yaml
    street: layers/highway/highway.yaml
    streetname: layers/highway_name/highway_name.yaml
    house: layers/building/building.yaml
    housenumber: layers/housenumber/housenumber.yaml
    place: layers/place/place.yaml

[nyurik]

Layer ID is used by other layers to establish dependencies, so each layer has to be reliably referenced. Won't implement