[feat] Add support for running_stage and current_fn in all Preprocess hook (1 / 2)

[tchaton]

What does this PR do?

This PR makes each Preprocess hook aware of its current function name and running_state.

class CustomPreprocess(Preprocess):

        def train_per_sample_transform_on_device(self, ...):
               assert self.training
               assert self.current_fn == "per_sample_transform_on_device"

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[codecov]

Codecov Report

Merging #200 (84eaa68) into master (62472d7) will increase coverage by 0.59%.
The diff coverage is 95.36%.

@@            Coverage Diff             @@
##           master     #200      +/-   ##
==========================================
+ Coverage   85.11%   85.70%   +0.59%     
==========================================
  Files          54       54              
  Lines        2391     2483      +92     
==========================================
+ Hits         2035     2128      +93     
+ Misses        356      355       -1     

Flag	Coverage Δ
unittests	85.70% <95.36%> (+0.59%)	⬆️

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

Impacted Files	Coverage Δ
flash/data/data_module.py	72.53% <ø> (ø)
flash/vision/classification/data.py	87.43% <85.29%> (-1.60%)	⬇️
flash/data/data_pipeline.py	87.36% <92.30%> (+0.18%)	⬆️
flash/data/auto_dataset.py	95.77% <92.85%> (-0.12%)	⬇️
flash/data/process.py	84.50% <97.43%> (+6.62%)	⬆️
flash/data/batch.py	76.85% <97.50%> (+6.26%)	⬆️
flash/core/classification.py	100.00% <100.00%> (ø)
flash/core/model.py	94.01% <100.00%> (+0.34%)	⬆️
flash/data/utils.py	96.84% <100.00%> (+4.38%)	⬆️
flash/tabular/classification/data/data.py	88.63% <100.00%> (ø)
... and 2 more

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