[mlir][IR] Combine location hash if required in OperationEquivalence::computeHash

This fixes a bug that `OperationEquivalence::computeHash` doesn't
combine hash of operation locations even when `IgnoreLocations` is false.
Added a unit test which fails at the current trunk.

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D154015