[MLIR][Presburger] Optimize for union & subtract

Added a series of optimization to the Subtract & Union function of PresburgerRelation, referring to the ISL implementation.
Add isPlainEqual to Subtract & union,also some basic check to union.
Tested it on a simple Benchmark implemented by myself to see that it can speed up the Subtract operation and Union operation, also decrease the result size.

The Benchmark can be found here: [[ https://github.com/gilsaia/llvm-project-test-fpl/blob/develop_benchmark/mlir/benchmark/presburger/Benchmark.cpp | benchmark]]

The overall results for Union & Subtract are as follows (previous benchmark has a bug,after fix that,the figure below is new)
{F28455229}

The results for each case are as follows
{F28455234}
{F28455239}

{F28455245}
{F28455246}

Reviewed By: Groverkss

Differential Revision: https://reviews.llvm.org/D156241