tokensByFormAll function
Builds a map from surface form → all tokens with that form, in order.
Implementation
Map<String, List<UDToken>> tokensByFormAll(List<UDToken> tokens) {
final map = <String, List<UDToken>>{};
for (final t in tokens) {
(map[t.form] ??= []).add(t);
final lower = t.form.toLowerCase();
if (lower != t.form) (map[lower] ??= []).add(t);
}
return map;
}