Add `json` format to `list` command

[alexlafroscia]

After finding #550 and the work that @musikid did toward resolving it, I decided to take a crack at getting that code working and merged.

Since the work from @musikid was a few years ago, all this PR is (so far) is getting that code into a mergable state and updating the tests so that they pass. At this point...

• [x] Build completes without errors
• [x] Tests all pass
• [ ] No clippy warnings

I'm going to iterate on this a bit, but figured I would open a PR so the the work being done is at least visible (and to put a little pressure on myself to actually finish this!)

---

The current output of the command, in JSON format, looks like this (taken from my own machine, so it reflects what I have installed locally):

{
  "runtimes": [
    {
      "source": "Default",
      "version": "16.13.2"
    }
  ]
},{
  "packages": [
    {
      "Default": {
        "details": {
          "name": "@fsouza/prettierd",
          "version": "0.18.1"
        },
        "node": "16.13.2",
        "tools": [
          "prettierd"
        ]
      }
    },
    {
      "Default": {
        "details": {
          "name": "@lifeart/ember-language-server",
          "version": "2.7.0"
        },
        "node": "16.13.2",
        "tools": [
          "ember-language-server"
        ]
      }
    },
    {
      "Default": {
        "details": {
          "name": "@tailwindcss/language-server",
          "version": "0.0.7"
        },
        "node": "16.13.2",
        "tools": [
          "tailwindcss-language-server"
        ]
      }
    },
    {
      "Default": {
        "details": {
          "name": "eslint_d",
          "version": "11.1.1"
        },
        "node": "16.13.2",
        "tools": [
          "eslint_d"
        ]
      }
    },
    {
      "Default": {
        "details": {
          "name": "svelte-language-server",
          "version": "0.14.18"
        },
        "node": "16.13.2",
        "tools": [
          "svelteserver"
        ]
      }
    },
    {
      "Default": {
        "details": {
          "name": "typescript",
          "version": "4.5.4"
        },
        "node": "16.13.2",
        "tools": [
          "tsc",
          "tsserver"
        ]
      }
    },
    {
      "Default": {
        "details": {
          "name": "typescript-language-server",
          "version": "0.9.4"
        },
        "node": "16.13.2",
        "tools": [
          "typescript-language-server"
        ]
      }
    },
    {
      "Default": {
        "details": {
          "name": "yarn-deduplicate",
          "version": "3.1.0"
        },
        "node": "16.13.2",
        "tools": [
          "yarn-deduplicate"
        ]
      }
    }
  ]
}

I'd like to alter this format somewhat, as there are a few things I think could be improved:

1. This mirrors the internal representation exactly, which I'm not sure is necessarily desirable. While all of the information you might want to consume is there, the structure isn't particularly self-descriptive; many objects with just a "Default" key in them pointing to a package doesn't really translate into something that's easily understood by whoever is reading the output. What else could be in that location? Why an array of objects with just one key? I think these are questions a user of this format would ask themselves
2. Returning multiple JSON objects, comma-separated, is going to be tough to parse. I think a single object with multiple top-level keys would make more sense. For example, if you try to pipe this into jq you end up with a parsing error right off the bat, because the comma after the runtimes object is not expected

Closes #550

[chriskrycho]

@alexlafroscia still interested in getting this across the line? If not, no worries. If so, I agree that the output should be valid JSON, so should probably be similar in spirit to the human and plain formats—it might warrant a bit of design discussion! Happy to help steward that forward if you want to tackle it, but again, no worries if not. Sorry this sat without reply for so long!