Ensure entities are copied during clone. (#134)

* Ensure entities are copied during clone.
* Organize cloned doc_gen properties for clarity.

Author: cpyle0819

aws_doc_sdk_examples_tools/doc_gen.py

@@ -172,10 +172,11 @@ def default(cls) -> "DocGen":
     def clone(self) -> "DocGen":
         return DocGen(
             root=self.root,
-            errors=MetadataErrors(),
             validation=self.validation.clone(),
             sdks={**self.sdks},
+            entities=self.entities,
             services={**self.services},
+            errors=MetadataErrors(),
             snippets={},
             snippet_files=set(),
             cross_blocks=set(),