Describe the feature request

WebNN CoreML backend doesn't support int64 data type, however some ops from ONNX produce int64 output, e.g. ArgMax, ArgMin, etc., CoreML's AragMax reproduces int32 output.

That means we should check the dimension size being reduced is within int32 range, then do type casting (int32 -> int64) for the output.

The node of such op must be the output of a subgraph model, as its next node is int64 input which is not supported by CoreML backend, and it will fall back, unless it is a special case: ArgMax-Cast (from int64 to int32).

Following actions can be taken into account:

• Use WebNN's opSupportLimits() to check if whether int64 data type is supported
• Make sure producing int32 output instead is safe
• Fuse ops for e.g. ArgMax-Cast(int64->int32)
• Convert int32 output tensor back to int64

Besides, how CoreML EP handles int64 data type would be a good reference.

Describe scenario use case

N/A