[ONNX] Update LayerNorm symbolic to handle autocasting (#52199) (#52350)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/52350
When onnx export creates a 0-dim tensor of constant type, this action overrides the type promotion logic as quoted in #9515. In order to prevent this from happening this PR adds the following functionality.
If the data type is a floating point type, it is converted to a 0-dim double tensor, else it is converted to a 0-dim tensor of its original type
Test Plan: Imported from OSS
Reviewed By: malfet
Differential Revision: D26490325
Pulled By: SplitInfinity
fbshipit-source-id: 4c47c69c9b6523d2e45b74c2541d6d8ca7e28fc9
