Automatically generate human-readable description of command

[pokey]

Like we do for generating spoken forms, we'd like to be able to generate a description of what a given command does. We could use this for

• the command decoder (eg the transcript in https://pokey.github.io/videos/op3VQvua67k/#bb592ada-3cb0-4bb4-93b4-aaf041ad7430)
• Generate cheatsheet extension-side #2099
• keyboard: add sidebar #2097
• Command examples in documentation
• Including them as a field in our recorded tests would make it clearer what they do for new users / contributors

For example:

{
    "name": "remove",
    "target": {
      "type": "primitive",
      "mark": {
        "type": "decoratedSymbol",
        "symbolColor": "default",
        "character": "a"
      },
      "modifiers": [
        {
          "type": "containingScope",
          "scopeType": {
            "type": "line"
          }
        }
      ]
    }
  }

would map to

"delete the line containing the token with a gray hat over the `a`"

Might be nice if the output could have a little structure, so that in rich contexts, eg web, it would render as

delete the line containing

Would also be good to support having placeholders at various places in a command. We could define a special symbol called PLACEHOLDER Eg

{
    "name": "remove",
    "target": {
      "type": "primitive",
      "mark": PLACEHOLDER,
      "modifiers": [
        {
          "type": "containingScope",
          "scopeType": {
            "type": "line"
          }
        }
      ]
    }
  }

would render to

"delete the line containing <mark>"

Note also that we may want to generate from the post-inference command 🤔