[LoopInterhcange] Handle movement of reduction phis appropriately

[LoopInterhcange] Handle movement of reduction phis appropriately

This patch fixes pr43326 and pr48212.

Currently when we move reduction phis to the right place,
loop interchange assumes the first phi in loop headers is
an induction phi, skips the first phi and assumes the rest
of phis are candidate reduction phis to move. However, it
may not always be the case.

This patch loops over all phis in loop headers and considers
a phi node as a candidate reduction phi to move only when it
is indeed a reduction phi across outer and inner loop.

Reviewed By: Whitney

Differential Revision: https://reviews.llvm.org/D102743