Add support for JsonStringEnumConverter<T> detection and test it (#1868)

Closes:
- #1867
- #1741

Author: wellWINeo

src/NJsonSchema.Tests/Generation/SystemTextJson/SystemTextJsonOptionsConverterTests.cs

@@ -72,6 +72,9 @@ public class AnnotatedPerson
 
             [JsonConverter(typeof(JsonStringEnumConverter))]
             public MyEnum StringEnum { get; set; }
+           
+            [JsonConverter(typeof(JsonStringEnumConverter<MyEnum>))]
+            public MyEnum StringEnum2 { get; set; }
 
             public MyEnum IntEnum { get; set; }
         }
@@ -103,6 +106,7 @@ public async Task SystemTextJson_WhenGeneratingWithCustomPropertyNames_ThenAttri
             Assert.True(schema.Properties.ContainsKey("NameLast"));
 
             Assert.True(schema.Properties["stringEnum"].ActualSchema.Type.HasFlag(JsonObjectType.String));
+            Assert.True(schema.Properties["stringEnum2"].ActualSchema.Type.HasFlag(JsonObjectType.String));
             Assert.True(schema.Properties["intEnum"].ActualSchema.Type.HasFlag(JsonObjectType.Integer));
         }
     }

src/NJsonSchema/Generation/ReflectionServiceBase.cs

@@ -379,7 +379,8 @@ private static bool HasStringEnumConverter(ContextualType contextualType)
                 if (jsonConverterAttribute?.ConverterType is Type converterType)
                 {
                     return converterType.IsAssignableToTypeName("StringEnumConverter", TypeNameStyle.Name) ||
-                           converterType.IsAssignableToTypeName("System.Text.Json.Serialization.JsonStringEnumConverter", TypeNameStyle.FullName);
+                           converterType.IsAssignableToTypeName("System.Text.Json.Serialization.JsonStringEnumConverter", TypeNameStyle.FullName) ||
+                           converterType.IsAssignableToTypeName($"System.Text.Json.Serialization.JsonStringEnumConverter`1[[{contextualType.OriginalType.AssemblyQualifiedName}]]", TypeNameStyle.FullName);
                 }
             }