title: Missing `.Relational()` method when migration from .NET Core 2.2 to 3.1
body: <p>I'm updating a project from 2.2 to 3.1 and I have the following method to automatically patch all <code>decimal</code> properties to use <code>decimal(18, 6)</code> sql type when creating new migrations.</p>
  
  <pre><code>    public static void PatchDecimalProperties(this ModelBuilder builder)
      {
          foreach (var property in builder.Model.GetEntityTypes()
              .SelectMany(t =&gt; t.GetProperties())
              .Where(p =&gt; p.ClrType == typeof(decimal) || p.ClrType == typeof(decimal?)))
          {
              property.Relational().ColumnType = "decimal(18, 6)";
          }
      }
  </code></pre>
  
  <p>Now in 3.1 the <code>IMutableProperty.Relational()</code> method does not exist anymore. </p>
  
  <p>Is this method still exists or is there a replacement? </p>