Render prefix ~ operator with a space - #2533

Fuzz round-trip found SELECT ~ -1 rendering as SELECT ~-1, which PostgreSQL retokenizes as the single ~- custom operator and fails to re-parse. SELECT ~ ~1 renders SELECT ~~1 and fails in every dialect, ~ @2 renders ~@2 and ~ #x renders ~# x in PostgreSQL.

Expr::UnaryOp display concatenates operator and operand in its final arm. BitwiseNot joins the spaced arm beside Not and Hash, the same remedy #2531 applies to @. Canonical output for SELECT ~expr becomes SELECT ~ expr, pinned with one_statement_parses_to in parse_generic_unary_ops.