Fix a bug in module deprecator (#3937)

Adds `__dict__` to the wrapped module to ensure its member attributes stay on it.

cirq/_compat.py

@@ -543,6 +543,8 @@ def _setup_deprecated_submodule_attribute(
     setattr(parent_module, old_child, new_module)
 
     class Wrapped(ModuleType):
+        __dict__ = parent_module.__dict__
+
         def __getattr__(self, name):
             if name == old_child:
                 _deduped_module_warn_or_error(

cirq/_compat_test.py

@@ -708,3 +708,16 @@ def test_subprocess_test_failure():
 
 def _test_subprocess_test_failure_inner():
     raise ValueError('this fails')
+
+
+def test_dir_is_still_valid():
+    subprocess_context(_dir_is_still_valid_inner)()
+
+
+def _dir_is_still_valid_inner():
+    """to ensure that create_attribute=True keeps the dir(module) intact"""
+
+    import cirq.testing._compat_test_data as mod
+
+    for m in ['fake_a', 'info', 'module_a', 'sys']:
+        assert m in dir(mod)