add VersionedSerialization + source generator

VersionedSerialization.Generator/Utils/CodeGenerator.cs

@@ -0,0 +1,54 @@
+using System.Text;
+
+namespace VersionedSerialization.Generator.Utils
+{
+    public class CodeGenerator
+    {
+        private const string Indent = "    ";
+
+        private readonly StringBuilder _sb = new();
+        private string _currentIndent = "";
+
+        public void EnterScope(string? header = null)
+        {
+            if (header != null)
+            {
+                AppendLine(header);
+            }
+
+            AppendLine("{");
+            IncreaseIndentation();
+        }
+
+        public void LeaveScope(string suffix = "")
+        {
+            DecreaseIndentation();
+            AppendLine($"}}{suffix}");
+        }
+
+        public void IncreaseIndentation()
+        {
+            _currentIndent += Indent;
+        }
+
+        public void DecreaseIndentation()
+        {
+            _currentIndent = _currentIndent.Substring(0, _currentIndent.Length - Indent.Length);
+        }
+
+        public void AppendLine()
+        {
+            _sb.AppendLine();
+        }
+
+        public void AppendLine(string text)
+        {
+            _sb.AppendLine(_currentIndent + text);
+        }
+
+        public override string ToString()
+        {
+            return _sb.ToString();
+        }
+    }
+}