Throws TypeError when top-level package.json does not exist

[FredKSchott]

Original Discussion: https://www.pika.dev/npm/@pika/pack/discuss/5
/cc @mmahandev, @FredKSchott

If no top-level package.json exists, we see this error:

TypeError: Cannot read property '@pika/pack' of undefined
    at Build.init (C:\Users\Reese\AppData\Roaming\npm-cache\_npx\8556\node_modules\@pika\pack\dist-node\index.js:2293:17)
    at <anonymous>

Instead, we should see something nice like:

Error: No top-level package.json manifest found. 
Exiting...