This change uses the recently-added equivalence relation class to
re-work the way synonyms between data values are managed by the fact
manager.
The tests for 'transformation_replace_id_with_synonym' have been
temporarily removed. This is because those tests are going to be
split into a number of test classes in an upcoming PR, once some other
refactorings have been applied, and it would be burdensome to
temporarily refactor all the tests to be in a working state for this
intermediate change.
This transformation can introduce an instruction that uses
OpCopyObject to make a copy of some other result id. This change
introduces the transformation, but does not yet introduce a fuzzer
pass to actually apply it.