libvterm: Update to 0.1.1 and change upstream source

Previously, we were using a neovim-maintained fork of upstream,
which these days is essentially a staging group before being
merged to the official repo. Releases come from the official
upstream, though, so this commit tracks that instead of cherry-picking
from the neovim repo.

While here, mark perl as being test-only.

PR: 240698
Submitted by: checo175 secmailpro
Approved by: maintainer