Update SequenceGeneratorDecoder to output predictions and probabilities

[jeffkinnison]

Predictor looks for <output_feature>.predictions and <output_feature>.probabilities in model output, however SequenceGeneratorDecoder.get_prediction_set only included logits. Excluding the others led to a KeyError when unflattening output features

File "/home/ray/anaconda3/lib/python3.8/site-packages/pandas/core/indexes/base.py", line 3623, in get_loc
    raise KeyError(key) from err
KeyError: 'title_probabilities' (type: RayTaskError(KeyError), retryable: true)

This update adds predictions and probabilities to get_prediction_set.

[github-actions]

Unit Test Results

         6 files  ±0           6 suites  ±0   5h 38m 48s ⏱️ + 4m 27s
  3 976 tests ±0    3 932 ✔️ ±0    44 💤 ±0  0 ❌ ±0 
11 949 runs  ±0  11 808 ✔️ ±0  141 💤 ±0  0 ❌ ±0 

Results for commit 5e5786c. ± Comparison against base commit ebaf32f.

♻️ This comment has been updated with latest results.