Separate applehelp to sphinxcontrib package

[tk0miya]

Feature or Bugfix

• Refactoring

Purpose

• refs: Split some builders and extensions to external package #4971

[codecov]

Codecov Report

Merging #5983 into master will increase coverage by 0.02%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #5983      +/-   ##
==========================================
+ Coverage   82.93%   82.95%   +0.02%     
==========================================
  Files         270      269       -1     
  Lines       39192    39045     -147     
  Branches     5868     5844      -24     
==========================================
- Hits        32502    32388     -114     
+ Misses       5334     5312      -22     
+ Partials     1356     1345      -11

Impacted Files	Coverage Δ
tests/test_build.py	97.36% <ø> (ø)	⬆️
sphinx/application.py	77.35% <ø> (ø)	⬆️
setup.py	0% <ø> (ø)	⬆️
sphinx/builders/applehelp.py	0% <0%> (-67.94%)	⬇️
sphinx/builders/html.py	83.68% <0%> (-0.12%)	⬇️

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