[perl #78194] Make sort copy PADTMPs

[perl #78194] Make sort copy PADTMPs

Copy PADTMPs (op return values) when there is a sort block/sub that is
not optimised away and we are not sorting in place, so that \$a == \$a
will return true.

Many ops return the same scalar each time, for efficiency; refgen (\)
knows about that and copies them, to hide the implementation detail,
but other ops (sort in this case) need to do the same thing.