Accept model type parameter in export_llama #4550

Job	Run time
build-benchmark-app / macos-job	23m 1s
build-demo-ios / macos-job	13m 7s
build-frameworks-ios / macos-job	27m 52s
upload-demo-ios	20s
test-demo-ios / mobile-job (ios)	14m 16s
upload-frameworks-ios	21s
	1h 18m 57s

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