Integrate pytest-faulthandler into the core

[nicoddemus]

• Add pytest-faulthandler files unchanged
• Adapt imports and tests
• Add code to skip registration of the external pytest_faulthandler
  to avoid conflicts

Fix #5440

[codecov]

Codecov Report

Merging #5441 into master will increase coverage by <.01%.
The diff coverage is 97.75%.

@@            Coverage Diff             @@
##           master    #5441      +/-   ##
==========================================
+ Coverage   96.03%   96.04%   +<.01%     
==========================================
  Files         115      117       +2     
  Lines       25512    25595      +83     
  Branches     2480     2486       +6     
==========================================
+ Hits        24501    24582      +81     
- Misses        706      707       +1     
- Partials      305      306       +1

Impacted Files	Coverage Δ
src/_pytest/config/__init__.py	94.62% <100%> (ø)	⬆️
src/_pytest/faulthandler.py	100% <100%> (ø)
testing/deprecated_test.py	100% <100%> (ø)	⬆️
src/_pytest/deprecated.py	100% <100%> (ø)	⬆️
testing/test_faulthandler.py	94.73% <94.73%> (ø)

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[nicoddemus]

Anymore reviewers? 😁

[Zac-HD]

Aside from the timeout type, this looks good to me.

[nicoddemus]

Implemented two small changes in the last commit, with the objective of simplifying the code:

• The --no-faulthandler option is not necessary given that we can use -p no:faulthandler.

• The --faulthandler-timeout command-line option has become an ini option, for the reasons described in Feature Request: Defining timeout via pytest.ini variable pytest-faulthandler#34. Users can still set it from the command-line using -o faulthandler_timeout, so no functionality is lost.

It seems the changes are innocuous and a step in the right direction of having less command-line options when existing options will do. I doubt if this will affect users much too.

Let me know if you have any objections, otherwise I plan to merge this soon. 😁