Document `signal.*` signals to fix Sphinx references

[LamentXU123]

in https://docs.python.org/3/library/signal.html we've got a document for every signal const like signal.SIGALRM, all supported signals are basically listed here
(except for user-defined signals and some other signals elsewhere)

however, there is no document for SIGQUIT, with every other const documented. This directly cause to a reference warning in sphinx build:

C:\Users\admin\Desktop\cpython-main\Doc\library\signal.rst:116: WARNING: py:const reference target not found: SIGQUIT [ref.const]

I'm now working on fixing the warning of this document, and I think we need a doc for SIGQUIT. Something like:

.. data:: SIGQUIT 

   Proccess quit.

   .. availability:: Unix.

Linked PRs

• gh-139843: Document signal.SIGQUIT to fix Sphinx references #139844
• [3.14] gh-139843: Document signal.SIGQUIT to fix Sphinx references (GH-139844) #139885
• [3.13] gh-139843: Document signal.SIGQUIT to fix Sphinx references (GH-139844) #139886
• gh-139843: Document signals (SIGSTOP, SIGVTALRM, SIGPROF) to fix sphinx references #139896
• [3.14] gh-139843: Document signals (SIGSTOP, SIGVTALRM, SIGPROF) to fix sphinx references (GH-139896) #139908
• [3.13] gh-139843: Document signals (SIGSTOP, SIGVTALRM, SIGPROF) to fix sphinx references (GH-139896) #139909

[picnixz]

I don't think we should just say "Process quit." I would copy whatever is said in the POSIX manual instead (see https://pubs.opengroup.org/onlinepubs/009695399/basedefs/signal.h.html)

[LamentXU123]

I don't think we should just say "Process quit." I would copy whatever is said in the POSIX manual instead (see https://pubs.opengroup.org/onlinepubs/009695399/basedefs/signal.h.html)

Terminal quit signal. will be better.