[GreedyPatternRewriter] Avoid reversing constant order

The previous fix from af371f9f only applied when using a bottom-up
traversal. The change here applies the constant preprocessing logic to the
top-down case as well. This resolves the issue with the canonicalizer pass still
reordering constants, since it uses a top-down traversal by default.

Fixes #51892

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D125623