Before, results from `dca` would look something like

    ## + py/meta/alerts/remote-flow-sources-reach

    - django/django@c2250cf_cb8f: tests/messages_tests/urls.py:38:16:38:48
        reachable with taint-tracking from RemoteFlowSource
    - django/django@c2250cf_cb8f: tests/messages_tests/urls.py:38:9:38:12
        reachable with taint-tracking from RemoteFlowSource

now it should make it easier to spot _what_ it is that actually changed,
since we pretty-print the node.

So it matches the new style we're using in aiohttp/twisted/...

Such that the result of `request.FILES["key"].file.read()` is tainted

since UploadedFile is the abstract base class, all real usage would be
of one of the subclasses, so removing this to not provide a false hope
that it actually works.

I don't think investing the time into making this work would give any
value, so that's why I didn't do it ;)

Like before, omitted ClassInstantiation

Having the additional taint step just next to the other definitions, so
everything is together.

InstanceSourceApiNode is a really good idea, but it just happened too
soon. I can't do what I need if I have to supply an API-node. So to
avoid confusion between deprecating to/from InstanceSource in those
classes, I opted to do some major reorganizing as well 👍

Due to aliasing restrictions, I had to use a little trick with the
`WerkzeugOld` module.

Also removed a misleading comment link to method on wrong class :D

I know that the TODO about not having the tools to handling
`meth = obj.meth; meth()` is outdated now that we `DataFlow::MethodCallNode`,
but I'm planning to deal with that later on ;)

It would probably have been easier to do this as the _first_ thing...
but that's too late now 😓

Such that it should be next to the other class-related predicates (such
as `instance()`), the class is called `AdditionalTaintStep`, and it
marked private.

I also moved any modeling of attributes as well, while I was at it.

A few stragglers that did not have the same TODO comments as the others

These were written way before the ones in DataFlowPrivate, but
apparently didn't cover quite as much :|

I realized that if you ever wanted to the way taint-steps works again,
you would have to go to all the 117 places it has been implemented, and
change EVERY ONE OF THEM :( so trying to solve that problem here.

Not super happy with the name, but that was just the best I could come up with :D