spectrogram and inverse spectrogram

[nihui]

• custom window
• padding for center=True
• padding pad_mode=reflect
• winlen normalized
• pnnx convert https://pytorch.org/audio/stable/generated/torchaudio.functional.spectrogram.html
• pnnx convert https://pytorch.org/audio/stable/generated/torchaudio.functional.inverse_spectrogram.html
• pnnx convert https://pytorch.org/audio/stable/generated/torchaudio.transforms.Spectrogram.html
• pnnx convert https://pytorch.org/audio/stable/generated/torchaudio.transforms.InverseSpectrogram.html
• pnnx fuse stft pattern
• pnnx ncnn stft test
• pnnx ncnn spectrogram test
• pnnx ncnn inverse spectrogram test
• doc
• coverage

notes

• only supports hann, hamming and all-one window
• inverse spectrogram does not support length parameter
• spectrogram always returns torch.view_as_real(out) as ncnn does not support complex typed mat yet
• inverse spectrogram always accepts torch.view_as_complex(in) as ncnn does not support complex typed mat yet

[tencent-adm]

All committers have signed the CLA.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 98.49246% with 3 lines in your changes missing coverage. Please review.

Project coverage is 89.99%. Comparing base (6a466ef) to head (68b3816).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
src/layer/inversespectrogram.cpp	97.97%	2 Missing ⚠️
src/layer/spectrogram.cpp	99.00%	1 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (6a466ef) and HEAD (68b3816). Click for more details.

HEAD has 31 uploads less than BASE

Flag	BASE (6a466ef)	HEAD (68b3816)
	32	1

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #5779       +/-   ##
===========================================
- Coverage   95.00%   89.99%    -5.02%     
===========================================
  Files         795      267      -528     
  Lines      271196    79032   -192164     
===========================================
- Hits       257640    71122   -186518     
+ Misses      13556     7910     -5646     

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