Added JsonResponse

[jxlil]

Added a JsonResponse subclass to facilitate parsing of response content

if isinstance(response, JsonResponse):
    data = response.jmespath('object.[*]')
    ...
elif isinstance(response, HtmlResponse):
    data = response.xpath('//p')
    ...
else:
    ...

Fixes #6069, closes #6171

[codecov]

Codecov Report

Merging #6174 (1fb611e) into master (fa690fb) will increase coverage by 0.02%.
Report is 5 commits behind head on master.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6174      +/-   ##
==========================================
+ Coverage   88.59%   88.62%   +0.02%     
==========================================
  Files         159      160       +1     
  Lines       11582    11611      +29     
  Branches     1885     1891       +6     
==========================================
+ Hits        10261    10290      +29     
  Misses        994      994              
  Partials      327      327              

Files	Coverage Δ
scrapy/http/__init__.py	100.00% <100.00%> (ø)
scrapy/http/response/json.py	100.00% <100.00%> (ø)
scrapy/responsetypes.py	91.78% <ø> (ø)

... and 11 files with indirect coverage changes

[wRAR]

Thanks!

[Gallaecio]

Thank you!!!