Support non-default negative axis value and intuitive data type combination for OneHot op

[hariharans29]

Description:
This change tries to resolve 2 open issues regarding the OneHot operator:

#1313 : Treat (non-default) negative axis value like how any other ONNX operator does
#1314 : Support a more intuitive data type combination for this operator

Motivation and Context
Resolve #1313 and #1314

[hariharans29]

CC: @fdwr

[pranavsharma]

Is this behavior documented in the spec? If not, can you document it?

[hariharans29]

Is this behavior documented in the spec? If not, can you document it?

This a good suggestion.

But this behavior is implicitly understood and expected of all ONNX ops that have an axis attribute/input. In fact, there are quite a few ONNX ops where this behavior is not explicitly stated but is handled anyway. For example, ArgMax, ArgMIn (to name a couple) have a similar expectation but have no such behavior explicitly documented. ONNXRuntime handles negative axis wherever an axis input is provided.

It might be worthwhile to state this just once somewhere in ONNX as opposed to adding one line for this op (and every other op that's missing the behavior explicitly)