Specification validation message customization with Func<>

[michalkowal]

Right now there is possibility to override validation message by use WithMessage function.

var spec = Specification.Length<string>(5).WithMessage("Incorrect value length");
spec.IsSatisfiedBy("lorem ipsum", out var result);    // "Incorrect value length"

There should be possibility to create validation message based on candidate value and specification parameters:

var spec = Specification.Length<string>(5)
    .WithMessage((c, p) => $"Incorrect value length - expected [{p["Length"]}] but passed [{c.Length}]");
spec.IsSatisfiedBy("lorem ipsum", out var result);    // "Incorrect value length - expected [5] but passed [11]"

Localization example:

public IValidationSpecification<string> CreateSpecification(IStringLocalizer localizer)
{
    return Specification.MaxLength<string>(100)
        .WithMessage((c, p) => localizer.GetString("Max length of value should be {1} but passed value has {0}",
            c.Length, p["MaxLength"]));
}