Implement Ada 2022 iterated assignment

Implement Ada 2022 iterated assignment

Ada 2022 includes iterated assignment for array initialization.  This
patch implements a subset of this for gdb.  In particular, only arrays
with integer index types really work -- currently there's no decent
way to get the index type in EVAL_AVOID_SIDE_EFFECTS mode during
parsing.  Fixing this probably requires the Ada parser to take a
somewhat more sophisticated approach to type resolution; and while
this would help fix another bug in this area, this patch is already
useful without it.