Package manager equivalent of pnpm exec, yarn exec, etc.

[benmccann]

The command provides a way to execute a locally installed package: https://pnpm.io/cli/exec

The Svelte CLI uses the package-manager-detector library to run such a command for any package manager, but the Deno version does not work/exist, which is preventing us from adding Deno support (sveltejs/cli#313 (review))

[bartlomieju]

I'm thinking that we could do deno task --eval "command" so we don't have to resort to adding a new subcommand.