[converter] added dtype support for oneHot for converter

[pyu10055]

parse the T param from the op definition and call tfjs-core onehot api accordingly.
fix #6773
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[Linchenn]

Could you add a param comment for dtype, at

tfjs/tfjs-core/src/ops/one_hot.ts

Lines 41 to 47 in e2b6a9d

	* @param indices `tf.Tensor` of indices with dtype `int32`. Indices must
	* start from 0.
	* @param depth The depth of the one hot dimension.
	* @param onValue A number used to fill in the output when the index matches
	* the location.
	* @param offValue A number used to fill in the output when the index does
	* not match the location.

[pyu10055]

Thanks, added.

Reviewable status: 0 of 1 approvals obtained (waiting on @jinjingforever)

[Linchenn]

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @jinjingforever)