[MLIR] PresburgerSet subtraction: fix bug where the set `b` was not restored properly on return

When subtracting `b \ c`, when there are divisions in `c`, these division
constraints get added to `b`. `b` must be restored to its original state
when returning, but these added divisions constraints were not removed in
one of the return paths. This patch fixes this and deduplicates the
restoration logic by encapuslating it in a lambda `restoreState`. The patch
also includes a regression test for the bug fix.

Reviewed By: Groverkss

Differential Revision: https://reviews.llvm.org/D115577