Allow referencing icons

[matkoniecz]

For example it would be nice if https://github.com/openstreetmap/id-tagging-schema/blob/main/data/presets/amenity/_coworking_space.json would be able to reference https://github.com/openstreetmap/id-tagging-schema/blob/main/data/presets/office/coworking.json

That would make changes like openstreetmap/id-tagging-schema#2064 less likely to cause accidental icon divergence

[matkoniecz]

See also https://github.com/openstreetmap/id-tagging-schema/pull/2147/changes#diff-3f4aafb5bc3fc1e07cd94a1d594424abf5f0082e57c13e816267c4b6a50e236d

It would be nice to reference in building type dropdown icons from specific building presets rather than define them twice

And openstreetmap/id-tagging-schema#2195