Most of a change's attributes are tenant-independent. This however is
different for topic dependencies, which should only be considered in
tenants where the dependencies-by-topic feature is enabled.
This is mainly a problem when a project is part of multiple tenants as
the dependencies-by-topic setting might be different for each tenant. To
fix this we will only return the topic dependencies for a change in
tenants where the feature has been activated.
Since the `needs_changes` property is now a method called
`getNeedsChanges()`, we also changed `needed_by_changes` to
`getNeededByChanges()` so they match.
Change-Id: I343306db0abbe2fbf98ddb3f81b6d509eaf4a2bf