Create Object that represents a Module (#18469)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18469
ghimport-source-id: 73cb8b58f43f10b1dcfca805fd5b25c4fa977632
Stack from [ghstack](https://github.com/ezyang/ghstack):
* **#18469 Create Object that represents a Module**
* #18468 slots with explicit value/setValue make more sense in future patches
* #18467 Make Object hold its ClassType
* #18379 Enforce single parent for script submodules
* #18378 Unify namespace of script::Module
* #18314 Add ability to specialize class types to ArgumentSpec
* #18226 Add Slot type to abstract the raw pointers being used for slots.
This changes the underlying storage for script::Module to hold
a ivalue::Object which has slots for all the parameters and attributes.
NamedIValue and Slot are now merged together into one class Slot that stores
the tuple (ivalue::Object, offset) and can be used to read the name, type,
or value of the slot and also to set the value. This cleans up a bunch
of client uses.
This PR does not actually use the module object in any generated code.
A future PR will switch how code is generated to treat modules as
first class.
Differential Revision: D14613508
fbshipit-source-id: d853a7559f58d244de2ef54a781427fcd1060ed0
