WIP: Support OS version in platform string #5712

Job	Run time
build (windows/amd64)	1m 45s
sandbox-build (linux/amd64)	6m 50s
build (freebsd/amd64)	1m 41s
sandbox-build (linux/arm64)	6m 37s
test-windows-amd64 (containerd, ./client)	5m 4s
test-freebsd-amd64	2m 33s
test-windows-amd64 (containerd, ./cmd/buildctl)	2m 57s
test-windows-amd64 (containerd, ./worker/containerd)	4m 8s
test-windows-amd64 (containerd, ./solver)	3m 19s
test-windows-amd64 (containerd, ./frontend)	1m 32s
test-windows-amd64 (containerd, ./frontend/dockerfile)	35m 47s
test-windows-amd64 (./..., 1)	4m 13s
	1h 16m 26s

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