[ONNX] Modified var_mean symbolic to support more combinations of dims (#48949)
Summary:
Based on existing implementation of var_mean, values of dim have to be sequential and start with zero. The formats listed below are cause scenarios with incompatible dimension for the Sub node.
-> dim[1, 2]
-> dim[0, 2]
-> dim[2, 0]
The changes in this PR allow such formats to be supported in var_mean
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48949
Reviewed By: houseroad
Differential Revision: D25540272
Pulled By: SplitInfinity
fbshipit-source-id: 59813a77ff076d138655cc8c17953358f62cf137
