This allows using npm deps of jsr deps without having to add them to the
root package.json.
Works by taking the package requirement and scanning the
`node_modules/.deno` directory for the best matching package, so it
relies on deno's node_modules structure.
Additionally to make the transition from package.json to deno.json
easier, Deno now:
1. Installs npm deps in a deno.json at the same time as installing npm
deps from a package.json.
2. Uses the alias in the import map for `node_modules/<alias>` for
better package.json compatiblity.
