Generate companion data from json

[ChizobaAmadi]

Is your feature request related to a problem? Please describe.
Hello,
I am currently working on implementing data synchronization. Since the server will receive partial data from clients, it will be nice to have a seamless way to map this data to drift.

Describe the solution you'd like
I propose adding an option in the build.yaml to create a fromJson method for the companion data class.

I have implemented a workaround following the guide in this previous issue, however, the solution is no longer as straightforward since I make use of DialectAwareSqlType type. For example:

/// columns: Derived from table.columnsByName.
/// data: The json to convert
Map<String, Expression> convertToExpressionMap(
    Map<String, GeneratedColumn> columns, Map<String, dynamic> data) {
  return data.map((key, value) {
    final column = columns[key];
    final variable = switch (column?.type) {
      genericDate => Variable(fallBackDate.read(value), genericDate),
      genericTimestampTz =>
        Variable(fallbackTimestampTz.read(value), genericTimestampTz),
      genericTimestamp =>
        Variable(fallbackTimestamp.read(value), genericTimestamp),
      _ => Variable(value)
    };

    return MapEntry(key, variable);
  });
}

I also ried simplifying the solution by using the typeMapping.read() but this expects to parse a dart type and not JSON.

It would be much better (developer-wise) and safer if the companion could support parsing JSON. Thanks !!