feat(task): Task description in the form of comments

[nathanwhit]

Closes #22786.

TLDR;

{
  "tasks": {
    // Some comment
    //
    // describing what the task does
    "dev": "deno run -A --watch main.ts"
  }
}

deno task

[bartlomieju]

LGTM, fun!

[dsherret]

FWIW, this could be further optimized to DenoSubcommand::Task(TaskFlags { task: None, .. }).

[nathanwhit]

I thought about that, but we also print available tasks when you try to run a task that doesn't exist. I guess we could just not show the comments then (or reparse the config?) but seemed more trouble than it's worth