add scores to Wav2Vec2WithLMOutput
Author: arampacha
Pull request: yes

# What does this PR do?

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- Adds `logit_score` and `lm_score` produced by `BeamSearchDecoderCTC` to `Wav2Vec2DecoderWithLMOutput`. Useful for results analysis and pseudo-labeling for self-training.
- Removes padding from batched logits (as returned by `Trainer.predict`) at `batch_decode`. This prevents producing nonsensical tokens at the end of decoded texts.


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## Who can review?

The PR is related to Robust ASR week.
@patrickvonplaten @anton-l

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Comments:
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