Add `MLFloat16` support for:
- `LayerNormalization`
- `SimplifiedLayerNormalization`
- `SkipLayerNormalization`
- `SkipSimplifiedLayerNormalization`
There are existing `LayerNormTest` unit tests that cover the `MLFloat16`
functionality for `LayerNormalization` once `MLFloat16` is registered
(for example
[`LayerNormTest.LayerNorm_Scale_Float16Input`](91c916f9c6/onnxruntime/test/contrib_ops/layer_norm_op_test.cc (L112))).
Similarly, there are unit tests such as
[`SkipLayerNormTest.SkipLayerNormBatch1_Float16`](91c916f9c6/onnxruntime/test/contrib_ops/skiplayernorm_op_test.cc (L255))
that cover MLFloat16 inputs for `SkipLayerNormalization`.
