toybox sh does not support leading left parenthesis in case syntax

[ScoreUnder]

test.sh:

case x in
  (x) echo Yep;;
esac

invocation: toybox sh test.sh

version: 0.8.7

expected: "Yep" on stdout; exit code 0

actual: sh: syntax error 'test.sh'@2: (

---

POSIX-compatible shells must support the optional leading left-parenthesis for each individual pattern: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_09_04_05. In practice this seems to hold true too; the posixy shells I've tried (mksh ksh zsh dash bash posh busybox) all conform to the expected behaviour.

I first encountered this testing against the dash-rc script here, which is also where I encountered #354.