feat(flags): improve help output and make deno run list tasks

[crowlKats]

• rewrite flag help
• use gray for indentation
• reorganize permission flags and split them up
• make help subcommand act like help flag
• deno run outputs list of tasks
• Fixes deno --help output unusable when redirected to a file #25120

error handling for deno run in case of no config file being found needs to be improved

[bartlomieju]

Running ./target/debug/deno run prints this:

./target/debug/deno run
error: deno task couldn't find deno.json(c). See https://docs.deno.com/go/config

This message is okay, but we could make it better. It should say that no argument was provided, deno tried to look up a config file and show list of available tasks and suggest to user that they might have wanted to run deno run ./script.ts of deno run dev (task name).

@crowlKats could you look into improving that one?

[bartlomieju]

LGTM