Reduce calls to ConcurrentDictionary to improve performance (#1464)

src/Generator/Generators/CSharp/CSharpMarshal.cs

@@ -351,9 +351,9 @@ namespace CppSharp.Generators.CSharp
             if (originalClass.IsRefType)
             {
                 Context.Before.WriteLine(
-                    "else if ({0}.NativeToManagedMap.ContainsKey({1}))", qualifiedClass, Context.ReturnVarName);
-                Context.Before.WriteLineIndent("{0} = ({1}) {2}.NativeToManagedMap[{3}];",
-                    ret, qualifiedIdentifier, qualifiedClass, Context.ReturnVarName);
+                    "else if ({0}.NativeToManagedMap.TryGetValue({1}, out var {2}))", qualifiedClass, Context.ReturnVarName, ret + "Object");
+                Context.Before.WriteLineIndent("{0} = ({1}) {2};",
+                    ret, qualifiedIdentifier, ret + "Object");
                 var dtor = originalClass.Destructors.FirstOrDefault();
                 if (dtor != null && dtor.IsVirtual)
                 {

src/Generator/Generators/CSharp/CSharpSources.cs

@@ -1909,13 +1909,12 @@ namespace CppSharp.Generators.CSharp
                 string.Join(", ", @params));
             WriteOpenBraceAndIndent();
 
-            WriteLine($"if (!NativeToManagedMap.ContainsKey({Helpers.InstanceField}))");
+            WriteLine($"if (!NativeToManagedMap.TryGetValue({Helpers.InstanceField}, out var {Helpers.TargetIdentifier}Object))");
             WriteLineIndent("throw new global::System.Exception(\"No managed instance was found\");");
             NewLine();
 
             var printedClass = @class.Visit(TypePrinter);
-            WriteLine($@"var {Helpers.TargetIdentifier} = ({
-                printedClass}) NativeToManagedMap[{Helpers.InstanceField}];");
+            WriteLine($@"var {Helpers.TargetIdentifier} = ({printedClass}){Helpers.TargetIdentifier}Object;");
             WriteLine("if ({0}.{1})", Helpers.TargetIdentifier, Helpers.OwnsNativeInstanceIdentifier);
             WriteLineIndent("{0}.SetupVTables();", Helpers.TargetIdentifier);
             GenerateVTableManagedCall(method);