[MLIR][NFC] Move PresburgerSet to Presburger/ directory

This patch moves PresburgerSet to Presburger/ directory. This patch is purely
mechincal, it only moves and renames functionality and tests.

This patch is part of a series of patches to move presburger functionality to
Presburger/ directory.

Reviewed By: arjunp

Differential Revision: https://reviews.llvm.org/D116836