[NNC] Make it able to normalize loop with variable start (#44133)
Summary:
Loops with variable start can also be normalized.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44133
Test Plan: updated testNormalizeStartVariable.
Reviewed By: navahgar
Differential Revision: D23507097
Pulled By: cheng-chang
fbshipit-source-id: 4e9aad1cd4f4a839f59a00bf8ddf97637a1a6648
