Interactive runner incompatible with experiments=beam_fn_api

When this is enabled one gets

```

ERROR: test_wordcount (apache_beam.runners.interactive.interactive_runner_test.InteractiveRunnerTest)
----------------------------------------------------------------------
Traceback
(most recent call last):
File "/Users/robertwb/Work/beam/incubator-beam/sdks/python/apache_beam/runners/interactive/interactive_runner_test.py",
line 85, in test_wordcount
result = p.run()
File "/Users/robertwb/Work/beam/incubator-beam/sdks/python/apache_beam/pipeline.py",
line 406, in run
self._options).run(False)
File "/Users/robertwb/Work/beam/incubator-beam/sdks/python/apache_beam/pipeline.py",
line 419, in run
return self.runner.run_pipeline(self, self._options)
File "/Users/robertwb/Work/beam/incubator-beam/sdks/python/apache_beam/runners/interactive/interactive_runner.py",
line 136, in run_pipeline
self._desired_cache_labels)
File "/Users/robertwb/Work/beam/incubator-beam/sdks/python/apache_beam/runners/interactive/pipeline_analyzer.py",
line 73, in __init__
self._analyze_pipeline()
File "/Users/robertwb/Work/beam/incubator-beam/sdks/python/apache_beam/runners/interactive/pipeline_analyzer.py",
line 93, in _analyze_pipeline
desired_pcollections = self._desired_pcollections(self._pipeline_info)

File "/Users/robertwb/Work/beam/incubator-beam/sdks/python/apache_beam/runners/interactive/pipeline_analyzer.py",
line 313, in _desired_pcollections
cache_label = pipeline_info.cache_label(pcoll_id)
File "/Users/robertwb/Work/beam/incubator-beam/sdks/python/apache_beam/runners/interactive/pipeline_analyzer.py",
line 397, in cache_label
return self._derivation(pcoll_id).cache_label()
File "/Users/robertwb/Work/beam/incubator-beam/sdks/python/apache_beam/runners/interactive/pipeline_analyzer.py",
line 405, in _derivation
for input_tag, input_id in transform_proto.inputs.items()
...
File
"/Users/robertwb/Work/beam/incubator-beam/sdks/python/apache_beam/runners/interactive/pipeline_analyzer.py",
line 405, in _derivation
for input_tag, input_id in transform_proto.inputs.items()
File "/Users/robertwb/Work/beam/venv3/bin/../lib/python3.6/_collections_abc.py",
line 678, in items
return ItemsView(self)
RecursionError: maximum recursion depth exceeded while
calling a Python object

```

Imported from Jira [BEAM-8436](https://issues.apache.org/jira/browse/BEAM-8436). Original Jira may contain additional context.
Reported by: robertwb.