fix: make --dry=json jq and JSON.parse-friendly

[jaredpalmer]

Allow --dry=json's stdout can be easily jq or JSON.parse'd.

Before

import { exec } from "child_process";

exec(
  "turbo run build --scope=app --since=HEAD^ --dry=json",
  (error, stdout, stderr) => {
    if (error) {
      console.error(`exec error: ${error}`);
      return;
    }

    const { packages } = JSON.parse(stdout);
    // JSON.parse error "• Packages changed since x in scope app" invalid json
  }
);

After

import { exec } from "child_process";

exec(
  "~/dev/vercel/turbo/cli/turbo run build --scope=storefront --since=HEAD^ --dry=json",
  (error, stdout, stderr) => {
    if (error) {
      console.error(`exec error: ${error}`);
      return;
    }

    const stuff = JSON.parse(stdout);
    // no error
  }
);

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[jaredpalmer]

(Initially i went to refactor ResolvePackages to make it a pure function, but given we are about to change everything with --filter, wasn't worth it)

[gsoltis]

I wouldn't mind just dropping the couple of output lines. I don't think they are adding much, since in the actual run case we print the packages in scope. We probably don't need to also repeat the user's flag values back to them.

[jaredpalmer]

Fair enough