Fix implicit non-trivial default ctor

src/Generator/AST/Utils.cs

@@ -30,7 +30,7 @@ namespace CppSharp.AST
             var isEmptyCtor = method.IsConstructor && method.Parameters.Count == 0;
 
             var @class = method.Namespace as Class;
-            if (@class != null && @class.IsValueType && isEmptyCtor && method.IsDefaulted)
+            if (@class != null && @class.IsValueType && isEmptyCtor && !@class.HasNonTrivialDefaultConstructor)
                 return true;
 
             if (method.IsDestructor)

tests/dotnet/CSharp/CSharp.Tests.cs

@@ -2050,7 +2050,6 @@ public unsafe class CSharpTests
     }
 
     [Test]
-    [Ignore("https://github.com/mono/CppSharp/issues/1777")]
     public void TestValueTypeStringMemberDefaultedCtor()
     {
         var test = new CSharp.ValueTypeNoCtor();

tests/dotnet/Common/Common.CSharp.csproj

@@ -1,5 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <LangVersion>10.0</LangVersion>
+    <LangVersion>11.0</LangVersion>
   </PropertyGroup>
 </Project>