Instead of passing `string` in the release tool for NPM dist tags, we
should use a union string type that limits the tags to `latest`, `next`
and anything matching `v{number}-lts`. This avoids mistakes at
compilation-level if an invalid/unknown tag would be set by a release
action.
PR Close#42133
We initially added logic for determining active release trains into
the merge script. Given we now build more tools that rely on this
information, we move the logic into a more general "versioning" folder
that can contain common logic following the versioning document for the
Angular organization.
PR Close#38656