refactor(serializer): utilize source-generated JSON context for serialization

Replaces manual `JsonSerializerOptions` configuration with source-generated `VersionVariablesJsonContext` for improved maintainability and performance. Removes obsolete private `JsonSerializerOptions` method and integrates the generated context in JSON methods.

Author: arturcic

src/GitVersion.Output/Serializer/VersionVariableSerializer.cs

@@ -1,5 +1,4 @@
 using System.IO.Abstractions;
-using System.Text.Encodings.Web;
 using GitVersion.Extensions;
 using GitVersion.Helpers;
 
@@ -9,8 +8,7 @@ internal class VersionVariableSerializer(IFileSystem fileSystem) : IVersionVaria
 {
     public static GitVersionVariables FromJson(string json)
     {
-        var serializeOptions = JsonSerializerOptions();
-        var variablePairs = JsonSerializer.Deserialize<Dictionary<string, string>>(json, serializeOptions);
+        var variablePairs = JsonSerializer.Deserialize(json, VersionVariablesJsonContext.Custom.DictionaryStringString);
         return FromDictionary(variablePairs);
     }
 
@@ -25,9 +23,7 @@ public string ToJson(GitVersionVariables gitVersionVariables)
             propertyInfo?.SetValue(variables, ChangeType(value, propertyInfo.PropertyType));
         }
 
-        var serializeOptions = JsonSerializerOptions();
-
-        return JsonSerializer.Serialize(variables, serializeOptions);
+        return JsonSerializer.Serialize(variables, VersionVariablesJsonContext.Custom.VersionVariablesJsonModel);
     }
 
     public GitVersionVariables FromFile(string filePath)
@@ -94,8 +90,6 @@ private void ToFileInternal(GitVersionVariables gitVersionVariables, string file
         fileSystem.File.WriteAllText(filePath, json);
     }
 
-    private static JsonSerializerOptions JsonSerializerOptions() => new() { WriteIndented = true, Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping, Converters = { new VersionVariablesJsonStringConverter() } };
-
     private static object? ChangeType(object? value, Type type)
     {
         if (!type.IsGenericType || type.GetGenericTypeDefinition() != typeof(Nullable<>)) return Convert.ChangeType(value, type);

src/GitVersion.Output/Serializer/VersionVariablesJsonContext.cs

@@ -0,0 +1,18 @@
+using System.Text.Encodings.Web;
+
+namespace GitVersion.OutputVariables;
+
+[JsonSourceGenerationOptions(
+    WriteIndented = true,
+    DefaultIgnoreCondition = JsonIgnoreCondition.Never,
+    Converters = [typeof(VersionVariablesJsonStringConverter)])]
+[JsonSerializable(typeof(VersionVariablesJsonModel))]
+[JsonSerializable(typeof(Dictionary<string, string>))]
+internal partial class VersionVariablesJsonContext : JsonSerializerContext
+{
+    public static VersionVariablesJsonContext Custom => field ??= new VersionVariablesJsonContext(
+        new JsonSerializerOptions(Default.Options)
+        {
+            Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping
+        });
+}

src/GitVersion.Output/Serializer/VersionVariablesJsonStringConverter.cs

@@ -31,5 +31,11 @@ public override void Write(Utf8JsonWriter writer, string? value, JsonSerializerO
         writer.WriteStringValue(value);
     }
 
+    public override string ReadAsPropertyName(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        => reader.GetString() ?? "";
+
+    public override void WriteAsPropertyName(Utf8JsonWriter writer, string value, JsonSerializerOptions options)
+        => writer.WritePropertyName(value);
+
     public override bool HandleNull => true;
 }