dynamic builders (#11)

- support `enum` type.
- support `struct` without builder.
- support `BlobArray<>` with element builder only (without `ArrayBuilder`)
  e.g. `BlobArray<BlobArray<BlobArray<int>>>` is valid now with only `IntBuilder`
- support `BlobPtr<>` without `PtrBuilder`

Author: quabug

Assets/Example.cs

@@ -29,6 +29,6 @@ public struct ExampleBlob
     public Guid Guid;
     [CustomBuilder(typeof(ObjectName))] public BlobString GameObjectName;
     public AnimationCurveBlob AnimationCurve;
-}
-
-public class ExampleBlobBuilder : BlobDataBuilder<ExampleBlob> {}
+    public ComponentType.AccessMode Enum;
+    public BlobArray<BlobArray<BlobArray<BlobPtr<BlobString>>>> Arrays;
+}