Introducing a [DebuggerTypeProxy] to the generated quantities (v6) (#1395)

This is the port of #1390 to v6

Author: lipchev

CodeGen/Generators/UnitsNetGen/QuantityGenerator.cs

@@ -35,6 +35,7 @@ public string Generate()
             Writer.WL(GeneratedFileHeader);
             Writer.WL(@"
 using System;
+using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Linq;");
@@ -66,6 +67,7 @@ namespace UnitsNet
             Writer.WLIfText(1, GetObsoleteAttributeOrNull(_quantity));
             Writer.WL(@$"
     [DataContract]
+    [DebuggerTypeProxy(typeof(QuantityDisplay))]
     public readonly partial struct {_quantity.Name} :
         {(_quantity.GenerateArithmetic ? "IArithmeticQuantity" : "IQuantity")}<{_quantity.Name}, {_unitEnumName}>,");