Checking `isSub` on the resulting bounds can have introduced new constraints,
which might allow us to replace the type parameter entirely.

In scala#20120, we reach constraints with equal bounds that are intersection types,
they are formed from multiple successive calls to `addOneBound`.

We miss the `replace` optimization in this case because
the bounds only become equal progressively, and
we are only checking for equality with the constraint being added.

The second tryReplace after updateEntry and isSub
does not address this specific issue but scala#19955.