Fix transformers optimizations for GPT-NeoX (#16743)
### Description
Fix some issues found in GPT-NeoX graph fusion:
(1) GPT-NeoX uses float16 weights. The step of using onnxruntime with
opt_level==1 uses CPU provider. Since most operators does not have fp16
in CPU EP, so extra Cast nodes are added to up cast to fp32.
(2) Add is shared by two LayerNormalization children, and
SkipLayerNormalization might cause invalid graph.
(3) Reshape fusion might miss since some part only check initializer but
not Constant.
This PR adds a check whether model uses FP16, and output a warning when
use_gpu is not True, and use GPU provider for graph optimization when use_gpu=True.
