Add support for brace-less hash patterns at top level of case/in.
`in a: x, b: y` is now equivalent to `in {a: x, b: y}`.
`in a:, b:` shorthand now works with newlines (CRuby compatible).
Changes:
- Add EXPR_VALUE to IS_LABEL_POSSIBLE() to recognize labels after `in`
- Add brace-less hash pattern rules to p_expr
- Change p_hash_elem to use p_as instead of p_expr to avoid recursion
- Add in_kwarg flag to parser state for pattern matching context
- Set in_kwarg in lexer when keyword_in is returned
- Use EXPR_ARG after tLABEL_TAG when in_kwarg is set (makes newlines significant)
Co-authored-by: Claude <noreply@anthropic.com>
Yukihiro "Matz" Matsumoto
e8096bf745