Include fully-qualified class name of contract classes in Dartdoc

[Albert221]

To avoid confusing different classes from contracts (or to be extra sure) we could include the FQCN in the Dartdoc of every class.

Right now:

/// LeanCode.Contracts.Security.AuthorizeWhenHasAnyOfAttribute('dealer')
@ContractsSerializable()
class SetPreferences with EquatableMixin implements Command {
  SetPreferences({
    required this.domesticOnly
    // (...)

My proposal:

/// Original FQCN: LeanCode.Cars.Contracts.Dealer.TopDeals.SetPreferences
///
/// Attributes:
/// * LeanCode.Contracts.Security.AuthorizeWhenHasAnyOfAttribute('dealer')
@ContractsSerializable()
class SetPreferences with EquatableMixin implements Command {
  SetPreferences({
    required this.domesticOnly
    // (...)