Determines the common path from a set of paths, using an optional separator, which defaults to the OS default separator.

      import { common } from "https://deno.land/std@0.138.0/path/mod.ts";
      const p = common([
        "./deno/std/path/mod.ts",
        "./deno/std/fs/mod.ts",
      ]);
      console.log(p); // "./deno/std/"