Issue a warning or fail if a specific file given as an entry point does not exist

[ptmkenny]

Simple knip.json:

{
  "entry": [
    "src/main.tsx!",
    "does-not-exist.ts",
  ]
}

does-not-exist.ts is a non-existent file. When you run npm run knip, there is no warning or error even though does-not-exist.ts does not exist.

It would be great if Knip had a check that issued an error or warning if any file specified as an entry point did not exist (and maybe also for regex if the regex had no match).

For large projects that change over time, I would prefer to get an error that could be caught in CI so that I could update the knip.config when I make major changes that affect the entry points.

[webpro]

Duplicate of #331. Agreed it's useful, but I currently just don't have the bandwidth to work on such nice-to-haves. It also requires work on the console streamer. Might pick it up later down the road.