Bug: Critical accuracy bugs for model_type=qwen2: no causal attention and wrong tokenizer

[michaelfeil]

What does this PR do?

What happend:
Qwen2Flash was written to support only Alibaba-NLP/gte-Qwen2-1.5B-instruct, which was trained and has reference inference code with causal=False (aka use_bidirectional_attention=True). Later on I asked to add a flag in the config to actually read this.
https://huggingface.co/Alibaba-NLP/gte-Qwen2-1.5B-instruct/discussions/28

Now, we have also newer models, e.g. jina which are built on qwen2 but with:

• causal=True
• no custom tokenizer.py
• affected: https://huggingface.co/jinaai/jina-code-embeddings-0.5b/blob/main/config.json, or nomic-ai/nomic-embed-code

The new models are currently loaded, but the output embeddings will be incorrect.

Fixes # (issue)

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[michaelfeil]

@codex review