Get topic name from base class to propagate remaps

[guilyx]

When remapping a topic foo to bar, it appears that Subscriber::getTopic returns the name of the topic as initialized when instantiating the subscriber foo. In the base class, get topic returns the remapped topic bar, which is in my opinion the correct behavior to go to.

If I were to retrieve the topic I'm subscribing to, I expect to retrieve the remapped name (aka the true name) rather than something that is not used.

[gbiggs]

@guilyx Could you please add a test that verifies the new behaviour?

[guilyx]

@gbiggs Sure, will take a few days