psql: Add leakproof indicator to \df+, \do+, \dAo+, and \dC+ output.

psql: Add leakproof indicator to \df+, \do+, \dAo+, and \dC+ output.

This allows users to determine whether particular functions are
leakproof, and whether the underlying functions used by operators and
casts are leakproof. This is useful to determine whether indexes can
be used in queries on security barrier views or tables with row-level
security policies.

Yugo Nagata, reviewed by Erik Wienhold and Dean Rasheed.

Discussion: https://postgr.es/m/20240701220817.483f9b645b95611f8b1f65da%40sranhm.sraoss.co.jp