[mlir][Sol] Lower concat builtin #56

Job	Run time
target-machine	4s
prepare-test-matrix	1m 0s
regression-tests (7690f3bb897fb2c40cb34a88d69a0039093d22fb, default)	16m 4s
check-formatting (7690f3bb897fb2c40cb34a88d69a0039093d22fb)	7m 8s
	24m 16s

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