[mlir][Interfaces] ValueBoundsOpInterface: Check if two values are equal

Add a helper function that computes if two SSA values have the same value, utilizing the `ValueBoundsOpInterface` infrastructure. Two SSA values have the same value, an equality bound of 0 can be derived for their subtraction.

The helper function can also be used to determine if two tensor dimension sizes are equal.

Differential Revision: https://reviews.llvm.org/D151443