Use JsonStringEnumConverter<T> instead of JsonStringEnumConverter (#1863)

Unlike JsonStringEnumConverter, the generic JsonStringEnumConverter<T> is AOT compatible.

This prevents the [SYSLIB1034](https://learn.microsoft.com/en-us/dotnet/fundamentals/syslib-diagnostics/syslib1034) warning to occur when System.Text.Json source generation is used.

Author: 0xced

src/NJsonSchema.CodeGeneration.CSharp.Tests/EnumTests.cs

@@ -115,6 +115,41 @@ public async Task When_enum_name_contains_colon_then_it_is_removed_and_next_word
             CSharpCompiler.AssertCompile(code);
         }
 
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task When_enum_is_string_then_generic_StringEnumConverter_is_used(bool nullable)
+        {
+            // Arrange
+            var json =
+                $$"""
+                {
+                    "type": "object",
+                    "additionalProperties": false,
+                    "properties": {
+                        "size" : {
+                            "type": [ "string"{{(nullable ? ", \"null\"" : "")}} ],
+                            "enum" : [
+                                "small",
+                                "medium",
+                                "large"
+                            ]
+                        }
+                    }
+                }
+                """;
+
+            var schema = await JsonSchema.FromJsonAsync(json);
+            var generator = new CSharpGenerator(schema, new CSharpGeneratorSettings { JsonLibrary = CSharpJsonLibrary.SystemTextJson });
+
+            // Act
+            var code = generator.GenerateFile("MyClass");
+
+            // Assert
+            await VerifyHelper.Verify(code);
+            CSharpCompiler.AssertCompile(code);
+        }
+
         public class MyStringEnumListTest
         {
             public List<MyStringEnum> Enums { get; set; }

src/NJsonSchema.CodeGeneration.CSharp.Tests/Snapshots/EnumTests.When_enum_is_string_then_generic_StringEnumConverter_is_used_nullable=False.verified.txt

@@ -0,0 +1,36 @@
+//----------------------
+// <auto-generated>
+// </auto-generated>
+//----------------------
+
+
+namespace MyNamespace
+{
+    #pragma warning disable // Disable all warnings
+
+    public partial class MyClass
+    {
+
+        [System.Text.Json.Serialization.JsonPropertyName("size")]
+        [System.Text.Json.Serialization.JsonConverter(typeof(System.Text.Json.Serialization.JsonStringEnumConverter<MyClassSize>))]
+        public MyClassSize Size { get; set; }
+
+    }
+
+    public enum MyClassSize
+    {
+
+        [System.Runtime.Serialization.EnumMember(Value = @"small")]
+        Small = 0,
+
+
+        [System.Runtime.Serialization.EnumMember(Value = @"medium")]
+        Medium = 1,
+
+
+        [System.Runtime.Serialization.EnumMember(Value = @"large")]
+        Large = 2,
+
+
+    }
+}

src/NJsonSchema.CodeGeneration.CSharp.Tests/Snapshots/EnumTests.When_enum_is_string_then_generic_StringEnumConverter_is_used_nullable=True.verified.txt

@@ -0,0 +1,36 @@
+//----------------------
+// <auto-generated>
+// </auto-generated>
+//----------------------
+
+
+namespace MyNamespace
+{
+    #pragma warning disable // Disable all warnings
+
+    public partial class MyClass
+    {
+
+        [System.Text.Json.Serialization.JsonPropertyName("size")]
+        [System.Text.Json.Serialization.JsonConverter(typeof(System.Text.Json.Serialization.JsonStringEnumConverter<MyClassSize>))]
+        public MyClassSize? Size { get; set; }
+
+    }
+
+    public enum MyClassSize
+    {
+
+        [System.Runtime.Serialization.EnumMember(Value = @"small")]
+        Small = 0,
+
+
+        [System.Runtime.Serialization.EnumMember(Value = @"medium")]
+        Medium = 1,
+
+
+        [System.Runtime.Serialization.EnumMember(Value = @"large")]
+        Large = 2,
+
+
+    }
+}

src/NJsonSchema.CodeGeneration.CSharp/Templates/Class.liquid

@@ -91,7 +91,7 @@
 {%-   endif -%}
 {%-   if property.IsStringEnum -%}
 {%-     if UseSystemTextJson -%}
-    [System.Text.Json.Serialization.JsonConverter(typeof(System.Text.Json.Serialization.JsonStringEnumConverter))]
+    [System.Text.Json.Serialization.JsonConverter(typeof(System.Text.Json.Serialization.JsonStringEnumConverter<{{ property.Type | rtrimquestionmark }}>))]
 {%-     else -%}
     [Newtonsoft.Json.JsonConverter(typeof(Newtonsoft.Json.Converters.StringEnumConverter))]
 {%-     endif -%}

src/NJsonSchema.CodeGeneration/DefaultTemplateFactory.cs

@@ -47,6 +47,7 @@ public DefaultTemplateFactory(CodeGeneratorSettingsBase settings, Assembly[] ass
             templateOptions.Filters.AddFilter("lowercamelcase", LiquidFilters.Lowercamelcase);
             templateOptions.Filters.AddFilter("uppercamelcase", LiquidFilters.Uppercamelcase);
             templateOptions.Filters.AddFilter("literal", LiquidFilters.Literal);
+            templateOptions.Filters.AddFilter("rtrimquestionmark", LiquidFilters.RightTrimQuestionMark);
 
             TemplateOptions = templateOptions;
         }
@@ -331,6 +332,12 @@ public static ValueTask<FluidValue> Literal(FluidValue input, FilterArguments ar
                 var converted = ConversionUtilities.ConvertToStringLiteral(input.ToStringValue(), "\"", "\"");
                 return new ValueTask<FluidValue>(new StringValue(converted, encode: false));
             }
+
+            public static ValueTask<FluidValue> RightTrimQuestionMark(FluidValue input, FilterArguments arguments, TemplateContext context)
+            {
+                var converted = input.ToStringValue().TrimEnd('?');
+                return new ValueTask<FluidValue>(new StringValue(converted, encode: false));
+            }
         }
 
         /// <summary>