cmd/go: support `@latest-prerelease` tag

[hyangah]

From #42545 (comment)

Use case
We have a group of VSCode plugin users who opted in to use prerelease versions of tools. For the users, this will be convenient. Currently the plugin has its own logic to retrieve the list, parse versions, and choose the highest tagged version (including prerelease), but it would be better if this can be done with go command.

[bcmills]

Compare #42545 (comment).

CC @jayconrod @matloob

[hyangah]

We are definitely in the second group - we want users to test the highest tagged version including prerelease.

[bcmills]

I don't think I would call it @latest-prerelease, though — that's a bit verbose. Maybe @prerelease?

I also wonder if we should change @v1.x to consider prereleases for v1.x if no release version for that minor is tagged. (Currently we interpret v1.x as ≥v1.x.0, which seems logical but I'm guessing isn't what users actually intend.)

[hyangah]

I am fine with any names. I think we need to be careful when choosing a name commonly used for branch.

No opinion on v1.x - to me that form looks like a shortcut of v1.x.0 (like the Go project itself) and should be considered a stable release.