[ONNX] Export and shape inference for prim uninitialized in If subblock (#46094)
Summary:
Enable export of prim::Uninitialized in If subblock outputs.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46094
Reviewed By: houseroad
Differential Revision: D24838537
Pulled By: bzinodev
fbshipit-source-id: d0719b140393595e6df114ef5cc1bb845e919c14
