[wip] Refactor Deserializer to be a DataSource / Input

[ananyahjha93]

What does this PR do?

Fixes #916

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[codecov]

Codecov Report

Merging #981 (18c8c96) into master (073166e) will decrease coverage by 0.07%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##           master     #981      +/-   ##
==========================================
- Coverage   88.26%   88.19%   -0.08%     
==========================================
  Files         250      250              
  Lines       13155    13184      +29     
==========================================
+ Hits        11611    11627      +16     
- Misses       1544     1557      +13     

Flag	Coverage Δ
unittests	88.19% <80.00%> (-0.08%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
flash/core/data/process.py	68.75% <80.00%> (+2.08%)	⬆️
flash/audio/speech_recognition/data.py	89.65% <0.00%> (-2.72%)	⬇️
flash/text/classification/model.py	91.83% <0.00%> (-0.76%)	⬇️
flash/text/classification/data.py	96.89% <0.00%> (-0.52%)	⬇️
flash/tabular/forecasting/data.py	94.82% <0.00%> (-0.26%)	⬇️
flash/tabular/data.py	95.00% <0.00%> (ø)
flash/core/utilities/types.py	100.00% <0.00%> (ø)
flash/tabular/forecasting/cli.py	100.00% <0.00%> (ø)
flash/audio/speech_recognition/cli.py	100.00% <0.00%> (ø)
flash/core/data/io/input.py	94.49% <0.00%> (+0.01%)	⬆️
... and 2 more

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[ethanwharris]

Adressed by #1013