zsh: support leading parens for zsh glob alternations and flags in command arguments

[LangLangBart]

Follow up to: #1276 (comment)

• ✅ 1cf3c19: added support for it inside [[ ]] test expressions

---

Usage in regular command arguments is not supported when ( is a leading paren

# Alternation
./shfmt -ln zsh <<<'echo (foo|bar).baz'
# <standard input>:1:6: a command can only contain words and redirects; encountered `(`

# Case-insensitive flag (requires EXTENDED_GLOB)
./shfmt -ln zsh <<<'setopt extendedglob; ls (#i)*.mod'
# <standard input>:1:25: a command can only contain words and redirects; encountered `(`