[Documentation] Explain Version Symbols for OperatorKernels.md

[axbycc-mark]

Describe the documentation issue

The OperatorKernels.md has three types of Opset Version entries.

1. Plain number, eg 13
2. List-like, eg [11, 18]
3. Plus symbol, eg 9+

I would like some clarification on the meanings, especially the plus symbol. For example, GridSample is listed as opset 16+ for the CUDA provider. I assumed this meant it was implemented for Opset 20 as well, but this seems not to be the case.

Page / URL

https://github.com/microsoft/onnxruntime/blob/rel-1.20.0/docs/OperatorKernels.md

[snnn]

I guess 16+ means 16.

See the comment at :

onnxruntime/onnxruntime/core/framework/kernel_registry.cc

Line 129 in 708ee85

// allow match if the kernel def has an end version. if it does not, all we know is that the kernel supported

[axbycc-mark]

Hmm, but why the plus sign?

[snnn]

By mistake.

We should clean up our kernel registration code in https://github.com/microsoft/onnxruntime/blob/main/onnxruntime/core/providers/cpu/cpu_execution_provider.cc so that the generated document would not have a plus sign there.