Themable, stretchable sdf highway shields (the number signs), optional multiline

[anderslund@expressional.social]

Themable, stretchable sdf highway shield icon (the number signs), optional multiline.
Unfortunately #MapLibreGL styles does not appear to support using "case" statements in "icon-color" (and "icon-halo-color") layers, forcing me to use multiple rules (for motorway, primary, other in this case).

The #OpenMapTiles OMT style (vectorstile used in https://osm.org) fails the multiline part, I used a poor mans replace:
`"text-field": ["join", ["split", ["to-string", ["get", "ref"]], ";"], "\n"],` to achieve that (the "ref" property in the vector tile is semicolon separated).

#openStreetMap