refactor: reorganize flags

- Prevent clap from auto-detecting terminal width and attempting to wrap
  text.
- Remove `--v8-options`, instead use `--v8-flags=--help`
- Give more descriptive names to unit tests in flags.rs
- Assume argv and subcommand into DenoFlags struct so the output of
  flags module is only DenoFlags rather than the tuple (subcommand, flags,
  argv).
- Improve CLI help text
- Make `deno run` specific args like `--allow-net` only show up in 'deno
  help run' instead of as global flags in `deno help`.
- Removes `deno version` to simplify our implementation and be closer to
  clap defaults. `deno -V` now only shows Deno's version and not V8's nor
  TypeScript. `Deno.versions` can be used to see that information.