readJson method
Reads a json file from the assets.
The fileName is the full path of the asset. When a package is given,
the path is resolved relative to that package's assets.
Implementation
Future<Map<String, dynamic>> readJson(
String fileName, {
String? package,
}) async {
final path = _resolve(fileName, package);
if (!_files.containsKey(path)) {
_files[path] = await _readJson(path);
}
assert(
_files[path] is _JsonAsset,
'"$path" was previously loaded as a different type',
);
return (_files[path]! as _JsonAsset).value;
}