title: Placeholders doesn't work in ValidationFailure message
body: <p>I'm trying to make <a href="https://github.com/JeremySkinner/FluentValidation/wiki/e.-Custom-Validators#using-a-custom-message-placeholder" rel="nofollow noreferrer">placeholders</a> work with my <code>ValidationFailure</code>. The below example is a simplified version of what's going on.</p>
  
  <pre><code>public IActionResult Get()
  {
      var errors = new List&lt;ValidationFailure&gt;();
      errors.Add(new ValidationFailure("PropertyName", "{PropertyValue} is not a valid value.", 42));
  
      var result = new ValidationResult(errors);
      result.AddToModelState(ModelState, null);
  
      return BadRequest(ModelState);
  }
  </code></pre>
  
  <p>Actual result:</p>
  
  <pre><code>{
      "PropertyName": [
          "{PropertyValue} is not a valid value."
      ]
  }
  </code></pre>
  
  <p>Expected result:</p>
  
  <pre><code>{
      "PropertyName": [
          "42 is not a valid value."
      ]
  }
  </code></pre>
  
  <p>I can see these methods on the <code>ValidationFailure</code> object. So I'm thinking I just need to send it to the right service to make the magic happen :)</p>
  
  <pre><code>/// &lt;summary&gt;
  /// Gets or sets the formatted message arguments.
  /// These are values for custom formatted message in validator resource files
  /// Same formatted message can be reused in UI and with same number of format placeholders
  /// Like "Value {0} that you entered should be {1}"
  /// &lt;/summary&gt;
  public object[] FormattedMessageArguments { get; set; }
  
  /// &lt;summary&gt;
  /// Gets or sets the formatted message placeholder values.
  /// &lt;/summary&gt;
  public Dictionary&lt;string, object&gt; FormattedMessagePlaceholderValues { get; set; }
  </code></pre>
  
  <p><a href="https://github.com/JeremySkinner/FluentValidation/blob/de244de630376a92b4e0a6fc0ad3c4e1f45f1182/src/FluentValidation/Results/ValidationFailure.cs#L79-L90" rel="nofollow noreferrer">source</a></p>
  
  <p>Any suggestions?</p>