Add bound check before bsearch() for performance

 Add bound check before bsearch() for performance
 
 In the current lazy vacuum implementation, some index AMs such as
 btree indexes call lazy_tid_reaped() for each index tuple during
 ambulkdelete to check if the index tuple points to the (collected)
 garbage tuple.  In that function, we simply call bsearch(), but we
 should be able to know the result without bsearch() if the index tuple
 points to the heap tuple that is out of range of the collected garbage
 tuples.  Therefore, add a simple bound check before resorting to
 bsearch().  Testing has shown that this can give significant
 performance benefits.
 
 Author: Masahiko Sawada <masahiko.sawada@2ndquadrant.com>
 Discussion: https://www.postgresql.org/message-id/flat/CA+fd4k76j8jKzJzcx8UqEugvayaMSnQz0iLUt_XgBp-_-bd22A@mail.gmail.com