fix(codegen): Adds access modifiers to serializable fields (#633)

- [X] Adds options for SerializableField.

Example:
```cs
[SerializableField(0, getter: "protected", setter: "protected", isVritual: true)]
private int _someField;
```

Defaults: `getter: "public", setter: "public", isVirtual: false`

Projects/SerializationGenerator/SourceGeneration/SourceGeneration.Class.cs

@@ -17,7 +17,7 @@ using System.Collections.Immutable;
 using System.Text;
 using Microsoft.CodeAnalysis;
 
-namespace SourceGeneration
+namespace SerializationGenerator
 {
     public static partial class SourceGeneration
     {
@@ -49,7 +49,7 @@ namespace SourceGeneration
         // TODO: Generalize this to any field using dynamic indentation
         public static void GenerateClassField(
             this StringBuilder source,
-            AccessModifier accessors,
+            Accessibility accessors,
             InstanceModifier instance,
             string type,
             string variableName,
@@ -63,7 +63,7 @@ namespace SourceGeneration
             }
 
             var instanceStr = instance == InstanceModifier.None ? "" : $"{instance.ToFriendlyString()} ";
-            var accessorStr = accessors == AccessModifier.None ? "" : $"{accessors.ToFriendlyString()} ";
+            var accessorStr = accessors == Accessibility.NotApplicable ? "" : $"{accessors.ToFriendlyString()} ";
             var valueStr = value == null ? "" : $" = {value}";
             source.AppendLine($"        {accessorStr}{instanceStr}{type} {variableName}{valueStr};");