Add ONNX export support for ModernBERT #36

Job	Run time
build (3.10, macos-15, test_modeling_gemma2.py)	1h 4m 14s
build (3.10, macos-15, test_modeling_gemma.py)	49m 55s
build (3.10, macos-15, test_modeling_llama.py)	11m 53s
build (3.10, macos-15, test_modeling_olmo.py)	13m 33s
build (3.10, macos-15, test_modeling.py)	10m 36s
build (3.10, macos-15, test_modeling_qwen2.py)	4m 15s
build (3.11, macos-15, test_modeling_gemma2.py)	58m 10s
build (3.11, macos-15, test_modeling_gemma.py)	47m 7s
build (3.11, macos-15, test_modeling_llama.py)	9m 0s
build (3.11, macos-15, test_modeling_olmo.py)	10m 31s
build (3.11, macos-15, test_modeling.py)	8m 45s
build (3.11, macos-15, test_modeling_qwen2.py)	3m 38s
build (3.12, macos-15, test_modeling_gemma2.py)	1h 2m 48s
build (3.12, macos-15, test_modeling_gemma.py)	53m 5s
build (3.12, macos-15, test_modeling_llama.py)	12m 49s
build (3.12, macos-15, test_modeling_olmo.py)	8m 8s
build (3.12, macos-15, test_modeling.py)	10m 53s
build (3.12, macos-15, test_modeling_qwen2.py)	3m 43s
	7h 23m 3s

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