Revert "refactor(cli): cleanup parse_args.ts (#4189)"

[kt3k]

This reverts commit 8c022c4.

fixes #4481

[iuioiua]

@timreichen, please feel free to reland your cleanup changes along with a passing test for the issue outlined in #4481.

[timreichen]

I think I found the bug. The aliasMap Set for key contains key itself. On that example header contains header as an alias.

Map(2) {
  "H" => Set(1) { "header" },
  "header" => Set(2) { "H", "header" }
}

This is fixed by filtering out the key.

before:

const set = new Set([key, ...aliases]);
aliases.forEach((alias) => aliasMap.set(alias, set));

after:

aliases.forEach((alias) => aliasMap.set(alias, new Set([key, ...aliases.filter((it) => it !== alias)])));

[timreichen]

PR #4487