oops

This PR ensures that if we release v3 in the future, that we don't use
`latest` as the npm tag, but `v3-lts` instead.

Unfortunately we can't just use `3` or `v3` because they are not valid
and you will get an error when trying to publish.

Angular uses `v{n}-lts` for the versions they still support:
https://www.npmjs.com/package/@angular/core?activeTab=versions

Adding a tag is important, because omitting the `--tag` is the same as
`--tag latest`

…19335)

The implementation of v3's math operator normalization uses a safe-list
of function names. Need to add `sibling-index()` and `sibling-count()`
to this list otherwise when used inside math functions like `calc()`
they'll get spaces around the `-`.