There are a lot of situations when we share the same pointer to a Bitmapset
structure across different places. In order to evade undesirable side effects
replace_relid() function should always return a copy.
Reported-by: Richard Guo
Discussion: https://postgr.es/m/CAMbWs4_wJthNtYBL%2BSsebpgF-5L2r5zFFk6xYbS0A78GKOTFHw%40mail.gmail.com Reviewed-by: Richard Guo, Andres Freund, Ashutosh Bapat, Andrei Lepikhov