[LT] Upstream TsNode, TsNodeLowering, TsLoweringContext (#68154)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/68154
Test Plan: added a basic test; cover more by using lazy_tensor_staging tests
Reviewed By: Krovatkin, alanwaketan
Differential Revision: D32224303
fbshipit-source-id: ac3e1161229b8ae60fdb15ffa72e17072b595914
