Add `IDomainResult.FailIfNull` methods (syntactic sugar)

[AKlaus]

Inspired by ArgumentNullException.ThrowIfNull() method in .NET 6 (docs)

Add syntactic sugar static methods to return Failed status if the specified parameter is null – all to save time writing a null check if condition.

Suggested methods:

• IDomainResult.FailIfNull(object? argument, string? errorMessage = default)
• DomainResult.FailIfNull(object? argument, string? errorMessage = default)

[AKlaus]

On second thought, the proposal would reduce understanding of the code and a marginal reduction of code lines.

Helper methods like this don't bring much value and may lead to an analysis paralysis on which method to use:

public static IDomainResult FailedIfNull<T>([NotNull] T? notNullArgument, string? error = null)
  => (notNullArgument is null) ? Failed(error) : Success(notNullArgument);