Fixes #24607.
This PR makes the logic that caches top level dependencies (things
present in import map) smarter, so we handle JSR dependencies without
root exports.
This PR implements the changes we plan to make to `deno install` in deno
2.0.
- `deno install` without arguments caches dependencies from
`package.json` / `deno.json` and sets up the `node_modules` folder
- `deno install <pkg>` adds the package to the config file (either
`package.json` or `deno.json`), i.e. it aliases `deno add`
- `deno add` can also add deps to `package.json` (this is gated behind
`DENO_FUTURE` due to uncertainty around handling projects with both
`deno.json` and `package.json`)
- `deno install -g <bin>` installs a package as a globally available
binary (the same as `deno install <bin>` in 1.0)
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Co-authored-by: Nathan Whitaker <nathan@deno.com>
