Add back StructWithPublicDefaultConstructor test (#65616)

Author: pedrobsaila

src/libraries/Microsoft.Extensions.DependencyInjection.Specification.Tests/src/ActivatorUtilitiesTests.cs

@@ -117,9 +117,7 @@ public void TypeActivatorWorksWithCtorWithOptionalArgs_WithStructDefaults(Create
             Assert.Null(anotherClass.ColorNull);
             Assert.Equal(12, anotherClass.Integer);
             Assert.Null(anotherClass.IntegerNull);
-            // re-enable once https://github.com/dotnet/csharplang/issues/99 is implemented
-            // see https://github.com/dotnet/runtime/issues/49069
-            // Assert.Equal(ExpectStructWithPublicDefaultConstructorInvoked, anotherClass.StructWithConstructor.ConstructorInvoked);
+            Assert.Equal(ExpectStructWithPublicDefaultConstructorInvoked, anotherClass.StructWithConstructor.ConstructorInvoked);
         }
 
         [Theory]

src/libraries/Microsoft.Extensions.DependencyInjection.Specification.Tests/src/Fakes/ClassWithOptionalArgsCtorWithStructs.cs

@@ -13,9 +13,7 @@ public class ClassWithOptionalArgsCtorWithStructs
         public int? Integer { get; }
         public int? IntegerNull { get; }
 
-        // re-enable once https://github.com/dotnet/csharplang/issues/99 is implemented
-        // see https://github.com/dotnet/runtime/issues/49069
-        //public StructWithPublicDefaultConstructor StructWithConstructor { get; }
+        public StructWithPublicDefaultConstructor StructWithConstructor { get; }
 
 #pragma warning disable SA1129
         public ClassWithOptionalArgsCtorWithStructs(
@@ -32,18 +30,28 @@ public ClassWithOptionalArgsCtorWithStructs(
             ConsoleColor? color = ConsoleColor.DarkGreen,
             ConsoleColor? colorNull = null,
             int? integer = 12,
-            int? integerNull = null
-            //StructWithPublicDefaultConstructor structWithConstructor = default
+            int? integerNull = null,
+            StructWithPublicDefaultConstructor structWithConstructor = default
         )
 #pragma warning restore SA1129
         {
             Color = color;
             ColorNull = colorNull;
             Integer = integer;
             IntegerNull = integerNull;
-            //StructWithConstructor = structWithConstructor;
+            StructWithConstructor = structWithConstructor;
         }
 
         public struct CustomStruct { }
+
+        public struct StructWithPublicDefaultConstructor
+        {
+            public bool ConstructorInvoked { get; private set; }
+
+            public StructWithPublicDefaultConstructor()
+            {
+                ConstructorInvoked = true;
+            }
+        }
     }
 }