Implement opset 15 #233
Description
https://github.com/onnx/onnx/blob/main/docs/Changelog.md#version-15-of-the-default-onnx-operator-set
Operators to update:
- CastLike
- Optional
- OptionalGetElement
- OptionalHasElement
- Pow
- Shape
Also:
- Update max supported opset constant