Support default args in symbolic tracing (#47615)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/47615
Test Plan: Imported from OSS
Reviewed By: Chillee
Differential Revision: D24865060
Pulled By: ansley
fbshipit-source-id: 32ff105a1fa9c4a8f00adc20e8d40d1b6bd7157f
