This commit modifies the ID calculation of normal tuples to just
use the alrady exisitng ItemPointer to offset the IV instead of
the actual offset addresses, as the ItemPointer doesn't change during
moves and also easier to use for replication.

As part of this, the structure of the IV is also changed: instead of
using the offset as the base number, and incrementing it sequentially,
we now insert the "base" ItemPointer at the high part of the IV, and
start the counter at the other end, at the low part of the IV.

This means that we are no longer using AES-CTR, but instead rely on a
custom AES based encryption, but this is also required for toast, as
with that, we can't rely on the uniqueness of the address in the entire
data range.

Old encryption tests are also deleted, as they no longer work with
these changes.