Let's split off a new vcs-tag option from version-tag that configures whether
the current commit should be appended to the version tag. Doing this saves
us from having to fiddle around with generating git versions in packaging
specs and instead let's meson do it for us, even if we pass in a custom
version tag.
With this approach there's no more need for tools/meson-vcs-tag.sh so
we remove it.
