[Refactor] Refactor data converter and gather

[Harold-lkk]

主要有以下更新：

1. 将 Gatherer 方法抽象成单独模块
2. 将 DataConverter 移除，其中的 pack_instance 抽象成 Packer
3. 将流程更改为

for split in splits
    self.obtainer()
    self.gatherer()
    self.parser()
    self.packer()
    self.dumper()

细微改动：

1. 规范 parser 的输入接口和输出接口：

• parse_files 输入统一为 img_paths, ann_paths:
  • 对于一个json 文件包含全部标注： img_paths 图像文件夹路径，ann_path 对应标注文件路径
  • 对于多个图像对应多个文件：img_paths 为图像路径列表，ann_paths 为对应图像列表
• 输出统一为list[tuple(图像路径，解析好的标注信息)]

2. Obtainer 增加了是否解压的判定，解压完成后增加一个 finsh.mmocr 文件

[gaotongxiao]

Invite @KevinNuNu to take a look

[codecov[bot]]

Codecov Report

Patch coverage: 75.47% and project coverage change: +2.04 :tada:

Comparison is base (62d440f) 88.08% compared to head (1c1cb07) 90.13%.

:exclamation: Current head 1c1cb07 differs from pull request most recent head 6bee8c0. Consider uploading reports for the commit 6bee8c0 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           dev-1.x    #1707      +/-   ##
===========================================
+ Coverage    88.08%   90.13%   +2.04%     
===========================================
  Files          176      190      +14     
  Lines        11022    11128     +106     
  Branches      1558     1567       +9     
===========================================
+ Hits          9709    10030     +321     
+ Misses        1022      790     -232     
- Partials       291      308      +17     

Flag	Coverage Δ
unittests	90.13% <75.47%> (+2.04%)	:arrow_up:

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

Impacted Files	Coverage Δ
...atasets/preparers/obtainers/naive_data_obtainer.py	16.82% <5.88%> (ø)
...r/datasets/preparers/packers/wildreceipt_packer.py	16.36% <16.36%> (ø)
mmocr/datasets/preparers/gatherers/naf_gatherer.py	31.42% <31.42%> (ø)
mmocr/datasets/preparers/parsers/coco_parser.py	18.00% <33.33%> (+0.69%)	:arrow_up:
mmocr/datasets/preparers/parsers/base.py	80.00% <77.77%> (+2.22%)	:arrow_up:
mmocr/utils/processing.py	79.31% <79.31%> (ø)
mmocr/datasets/preparers/dumpers/base.py	80.00% <80.00%> (ø)
mmocr/datasets/preparers/packers/base.py	81.25% <81.25%> (ø)
...ocr/datasets/preparers/packers/textrecog_packer.py	81.25% <81.25%> (ø)
mmocr/datasets/preparers/data_preparer.py	83.67% <81.81%> (+15.49%)	:arrow_up:
... and 25 more

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