Attention sink support for LLM runner #1807

Job	Run time
test-xnnpack / test-backend-linux (xnnpack, models) / linux-job	55m 6s
test-xnnpack / test-backend-linux (xnnpack, operators) / linux-job	14m 29s
test-xnnpack / test-backend-macos	0s
test-xnnpack / package-golden-artifacts	3m 43s
	1h 13m 18s

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