Add fusions for OpenAI CLIP (#20721)
### Description
This PR adds fusions for [OpenAI's CLIP
model](https://huggingface.co/openai/clip-vit-large-patch14-336). Here
is an example of how to run the ORT transformer optimizer for the linked
CLIP model.
```
$ git clone https://github.com/microsoft/onnxruntime
$ cd onnxruntime/onnxruntime/python/tools/transformers
$ python3 optimizer.py --input /path/to/model.onnx --output /path/to/model_opt.onnx --model_type clip --num_heads 16 --hidden_size 1024 --use_external_data_format --opt_level 0
```
### Motivation and Context
This PR helps optimize multi-modal models that use CLIP for the vision
encoder.
