[DML] Add FastGelu

[PatriceVignola]

Although DML doesn't have a "fast" gelu approximation operator, its standard GELU operator is still faster than having to combine all the separate elementwise operators from different ops.

[sumitsays]

    ML_CHECK_VALID_ARGUMENT(kernelCreationContext.GetOutputCount() == 1);

As bias is an optional input for FastGelu, this check will fail for FastGelu when bias won't be present.

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Refers to: onnxruntime/core/providers/dml/DmlExecutionProvider/src/Operators/DmlOperatorBiasGelu.cpp:16 in e745456. [](commit_id = e745456, deletion_comment = False)

[sumitsays]