Confusing naming for argument `n_stft` in MelScale

🐛 Describe the bug

The name and docstring of the argument n_stft in MelScale is confusing, because:

• Just seeing the name, it looks equivalent to n_fft (just changes from FFT to STFT), which is a typical name used for the FFT size. Actually it is used with that purpose in torchaudio Spectrogram and librosa.feature.melspectrogram.
• Moreover, the docstring for n_stft explicitly states "See n_fft in :class:Spectrogram", which looks as a confirmation that n_stft is indeed the FFT size.

IMO, a more appropriate name for this argument would be something like n_freqs. Actually, it is under that name in torchaudio.functional.melscale_fbanks

Versions

torch 2.0.0+cu117
torchaudio 2.0.1+cu117

(I think nothing else is relevant)

Start with src/torchaudio/transforms/_transforms.py, reading the MelScale argument and docstring cited in the issue, then compare the n_freqs naming in src/torchaudio/functional/functional.py at melscale_fbanks. Check related tests and call sites to understand the naming impact; done means the argument documentation and naming clearly distinguish frequency-bin count from FFT size.