Implement opset 16

[Swopper050]

https://github.com/onnx/onnx/blob/main/docs/Changelog.md#version-16-of-the-default-onnx-operator-set

Operators to update:

• GreaterOrEqual
• LeakyRelu
• LessOrEqual
• PRelu
• Where
• Identity

Also:

• Update max supported opset constant