fix(cli) error gracefully when script arg is not present and `--v8-flags` is present in `deno run` (#20145)

Fix #20022, fix #19627 (duplicate)

#17333 upgraded clap from version 3.1 to version 4. clap version 3.2.0
(intentionally) broke a behavior that deno was relying on to make `deno
run --v8-flags=--help` work without specifying a file, see
clap-rs/clap#3793. The workaround was to make the script argument
required _unless_ `--v8-flags` is present. This broke the expectation
that all successfully parsed `run` commands have the script argument
set, leading to the panic on
`matches.remove_many::<String>("script_arg").unwrap()`.

Clap, as far as I was able to find out, does not currently offer a neat
solution to this problem. This PR adds logic to create and return a
custom clap error when a parsed run command does not have the script
argument.

I added an appropriate test.

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