Lock ops based on computed key rather than LLB digest #646

Job	Run time
prepare	5s
test / prepare	3m 48s
binaries (darwin/amd64)	9m 47s
binaries (darwin/arm64)	3m 17s
binaries (linux/amd64)	3m 19s
binaries (linux/arm/v7)	11m 44s
binaries (linux/arm64)	9m 19s
binaries (linux/s390x)	11m 45s
binaries (linux/ppc64le)	3m 24s
binaries (linux/riscv64)	29s
binaries (windows/amd64)	3m 5s
binaries (windows/arm64)	3m 8s
test / run (containerd, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	38m 23s
test / run (containerd-rootless, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integr...	38m 54s
test / run (containerd-1.6, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	37m 20s
test / run (containerd-snapshotter-stargz, ./client ./cmd/buildctl ./worker/containerd ./solver ./fronte...	36m 58s
test / run (oci, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	42m 24s
test / run (oci-rootless, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	37m 4s
test / run (oci-snapshotter-stargz, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, int...	42m 17s
test / run (./..., 1, integration gateway)	37m 18s
test / run (./client, containerd, nydus, integration)	8m 12s
test / run (./client, oci, nydus, integration)	7m 2s
test / run (./..., nydus, 1, integration)	39m 3s
image	0s
release	0s
	7h 8m 5s

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