Add support for Double2/3/4 for Variant

Increase size to 40 bytes to store Double3 without allocations
Change Ray and BoundingBox to be stored inlined in BoundingBox
Use safer accessors to read Variant explicit data type

Source/Editor/Utilities/VariantUtils.cs

@@ -60,6 +60,10 @@ namespace FlaxEditor.Utilities
 
             Int16,
             Uint16,
+
+            Double2,
+            Double3,
+            Double4,
         }
 
         internal static VariantType ToVariantType(this Type type)