This generalizes the indir reordering optimization (that currently only
triggers for loads) to kick in for GT_STOREIND nodes.

The main complication with doing this is the fact that the data node of
the second indirection needs its own reordering with the previous
indirection. The existing logic works by reordering all nodes between
the first and second indirection that are unrelated to the second
indirection's computation to happen after it. Once that is done we know
that there are no uses of the first indirection's result between it and
the second indirection, so after doing the necessary interference checks
we can safely move the previous indirection to happen after the data
node of the second indirection.

…rs-adjacent