Hojun-Cho
dd188ca460
`e is T` returns bool (variant tag == T's index); `e as T` unwraps to T or exit(1) on mismatch. Postfix, same precedence as `:` cast. TK_IS / N_TYPETEST / N_TYPEASSERT appended at the tail of their enums so every prior numeric value stays unchanged — the 990_selfhost wwdump-diff stays byte-clean. Cgen mirrors the match-case slot-based load (tag at +0, value at +8/+16), so an N_IDENT tagged-union local works just like a match scrutinee. Selfhost cgen inlines the slot resolution because the wwstage cgen drops sign bits on `*i32` output parameters in this position. Renames `errors.is` -> `errors.equal` (the only naming collision; the existing comment already noted it shared shape with strings.equal/bytes.equal).