[Refactor] Refactor TPS

[Mountchicken]

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[gaotongxiao]

Since pytorch 1.3, the default behavior of grid_sample has been changed. Keeping align_corners=True is empirically crucial to the performance of STN

[codecov]

Codecov Report

Base: 85.38% // Head: 85.56% // Increases project coverage by +0.17% 🎉

Coverage data is based on head (969b36c) compared to base (b8c445b).
Patch coverage: 94.95% of modified lines in pull request are covered.

❗ Current head 969b36c differs from pull request most recent head 5511c06. Consider uploading reports for the commit 5511c06 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           dev-1.x    #1240      +/-   ##
===========================================
+ Coverage    85.38%   85.56%   +0.17%     
===========================================
  Files          160      162       +2     
  Lines         9994    10111     +117     
  Branches      1388     1391       +3     
===========================================
+ Hits          8533     8651     +118     
+ Misses        1215     1212       -3     
- Partials       246      248       +2     

Flag	Coverage Δ
unittests	85.56% <94.95%> (+0.17%)	⬆️

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

Impacted Files	Coverage Δ
...odels/textrecog/preprocessors/base_preprocessor.py	83.33% <83.33%> (ø)
...models/textrecog/preprocessors/tps_preprocessor.py	95.57% <95.57%> (ø)
mmocr/datasets/transforms/textrecog_transforms.py	91.74% <0.00%> (-8.26%)	⬇️
mmocr/datasets/preparers/parsers/base.py	72.00% <0.00%> (-5.78%)	⬇️
...r/models/kie/postprocessors/sdmgr_postprocessor.py	92.64% <0.00%> (+7.35%)	⬆️
...cr/models/textdet/module_losses/pan_module_loss.py	96.79% <0.00%> (+7.69%)	⬆️

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[gaotongxiao]

@Mountchicken You can merge this PR with the latest dev-1.x branch before I proceed to merge