The following changes make the predicate locking functions more
generic and suitable for use by future access methods:

- PredicateLockTuple() is renamed to PredicateLockTID().  It takes
  ItemPointer and inserting transaction ID instead of HeapTuple.

- CheckForSerializableConflictIn() takes blocknum instead of buffer.

- CheckForSerializableConflictOut() no longer takes HeapTuple or buffer.

Author: Ashwin Agrawal
Reviewed-by: Andres Freund, Kuntal Ghosh, Thomas Munro
Discussion: https://postgr.es/m/CALfoeiv0k3hkEb3Oqk%3DziWqtyk2Jys1UOK5hwRBNeANT_yX%2Bng%40mail.gmail.com