feat: add `deno ci` subcommand (#34235)
Adds `deno ci`, a thin subcommand for reproducible installs in CI
environments. It mirrors `npm ci`: errors if `deno.lock` is missing,
removes any existing `node_modules` directory, then runs the install
with `--frozen` so the lockfile must match the config file exactly.
The intent is to give CI scripts and Dockerfiles an obvious,
greppable signal of "reproducible install" without having to remember
the right combination of flags on `deno install`.
`--prod` and `--skip-types` are accepted with the same semantics as
`deno install`.
