Feat: Add a way to detect if a file is run by deno serve or deno run

[ArmaanAS]

Add a way to detect if a file is run by deno serve or deno run.

Maybe add a variable like Deno.subcommand which has the type

declare namespace Deno {
  export const subcommand: "run" | "serve" | "task" | "test" | "bench" | "jupyter" | "repl" | "eval" | "install" | "uninstall" | "add" | "remove";
}

In production I want to use deno serve --parallel but locally I want to to use Deno.serve(). The reason is a bit complicated but basically my default export takes 5-10 seconds before it's exported which delays deno serve starting the server by over 5 seconds, however using Deno.serve() allows me to start the server almost instantly. In production I don't have the delay.

(N.B. I can't switch to deno serve at all because of this blocker #24099 but I want to!.)

[CyanChanges]

@ArmaanAS @littledivy Can you provide an example of how to use this variable? It should be a static variable that can be accessed from anywhere in the code or part of a trait.

It should be like this.

if (Deno.subcommand === "serve") {

} else {
  
}

I'll do it.

So, is there any update on this?