cmd/vet, x/tools/internal/versions: fix interpretation of empty language version

[timothy-king]

x/tools/internal/versions currently interprets invalid/unknown language versions ("") as some unknown earliest version. go/types interprets an unknown language version as "an empty string disables Go language version checks" and treats this as if all language features are allowed. This is closer to treating this as if it is some unknown future version. x/tools should be consistent with go/types.

Users of internal/versions x/tools/go/analysis/passes/loopclosure and x/tools/go/ssa need to update their interpretation.

Related #65612.

[gopherbot]

Change https://go.dev/cl/567635 mentions this issue: internal/versions: updates the meaning of FileVersions.

[dmitshur]

@timothy-king This issue is described to be for x/tools. Was it added to Go1.22.1 milestone by mistake, and can be Unreleased instead? Thanks.

[timothy-king]

It probably should be cherry picked into cmd/vet as a bug fix.

[dmitshur]

Ok, that involves more steps, please see https://go.dev/wiki/MinorReleases.
Since this is the main tracking issue, let's move it to the Go1.23 milestone.