[pytorch][codegen] add fully migrated scripts to mypy strict config (#47747)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47747
Moved MANUAL_AUTOGRAD / etc to gen_trace_type.py to avoid mypy from
scanning not yet migrated gen_variable_type.py.
Differential Revision: D24885066
Test Plan: Imported from OSS
Reviewed By: ezyang
Pulled By: ljk53
fbshipit-source-id: bf420e21c26f45fe2b94977bc6df840ffd8a3128
