Support for Rector 0.17.3

[driftingly]

It looks like Rector is moving away from BetterNodeFinder.
Lots of deprecated methods: rectorphp/rector#7947

We'll need to update calls to $this->betterNodeFinder->*.

[GeniJaho]

Do you have any suggestions about finding parents of classes? With BetterNodeFinder it was a one-liner but now we have to rely on reflection, which adds a few extra lines and cases to think about. I'm working on updating the rules dependent on BetterNodeFinder but not sure if there's a better way.

Also not sure if there are any performance penalties if we use AbstractScopeAwareRector instead of AbstractRector 👀.

[driftingly]

Thanks for all your work on this @GeniJaho 🙌