] Auto-generate stubs for named_resources (attempt2) (#1161)

Summary:


Internal
Generate stubs for all the methods generated by the decorator of `named_resources`.

Previous attempt reverted D83985902 because of autodeps issues. 
Genrule that looks at the all the named_resources and generates a file `named_resources.pyi` which is used by the test. 


Three targets added
1. `//torchx/fb/stubgen:generate_named_resources_stub`
2. `//torchx/specs:named_resources_stubs`

Introduce a .bzl file and wrapper for our usecase so we can share srcs and deps among two python libraries
1. //torchx/specs:lib_core_srcs - which is used by the other target `//torchx/fb/stubgen:generate_named_resources_stub` to create the stubs
2. //torchx/specs:lib_core - which is as before but with the additional type_stubs included. 

Additionally,
Modify some named resources as well.
Fix some imports for completion

Differential Revision: D86111386

Author: AbishekS

torchx/specs/test/named_resources_test.py

@@ -8,7 +8,6 @@
 # pyre-strict
 
 
-import os
 import unittest
 from unittest.mock import MagicMock, patch