[MLIR] Add clearAndCopyFrom to IntegerPolyhedron

This patch adds clearAndCopyFrom to IntegerPolyhedron. This requires moving
LLVM-style RTTI from FlatAffineConstraints to IntegerPolyhedron.

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

Reviewed By: arjunp

Differential Revision: https://reviews.llvm.org/D116533