LaTeX: separate terms from their definitions by a CR (close #9985)

[jfbu]

Close #9985

Also, in passing, this adds better rendering of glossary terms with a common definition (less vertical whitespace):
Fix #10000

Hence both Bugfix (too much whitespace between glossary terms sharing common definitionà) and New feature (separate terms from defintions by a CR in pdf output).

As far as I tested briefly, this does not cause breakage if used with numpy's hack into LaTeX description lists, but the hack of their project should be removed entirely, as it causes bad extraneous vertical whitespace.

Related #9988

[jfbu]

I used this test:

Listing:

:samp:`{file}.cc` :samp:`{file}.cp` :samp:`{file}.cxx` :samp:`{file}.cpp` :samp:`{file}.CPP` :samp:`{file}.c++` :samp:`{file}.C`
  C++ source code that must be preprocessed.  Note that in :samp:`.cxx`,
  the last two letters must both be literally :samp:`x`.  Likewise,
  :samp:`.C` refers to a literal capital C.

:samp:`{file}.mm` :samp:`{file}.M`
  case1:
    Objective-C++ source code that must be preprocessed.
  case2:
    Objective-C++ source code that must be preprocessed.


:samp:`{file}.mii`
  Objective-C++ source code that should not be preprocessed.

:samp:`{file}.hh` :samp:`{file}.H` :samp:`{file}.hp` :samp:`{file}.hxx` :samp:`{file}.hpp` :samp:`{file}.HPP` :samp:`{file}.h++` :samp:`{file}.tcc`
  C++ header file to be turned into a precompiled header or Ada spec

test
  hello
    again

  hello
    again


indented

  more test
    hello
      again

    hello [1]_
      again

    hello
      again

      :samp:`{file}.cc` :samp:`{file}.cp` :samp:`{file}.cxx` :samp:`{file}.cpp` :samp:`{file}.CPP` :samp:`{file}.c++` :samp:`{file}.C`
        C++ source code that must be preprocessed.  Note that in :samp:`.cxx`,
        the last two letters must both be literally :samp:`x`.  Likewise,
        :samp:`.C` refers to a literal capital C.

      :samp:`{file}.mm` :samp:`{file}.M`
        case1:
          Objective-C++ source code that must be preprocessed.
        case2:
          Objective-C++ source code that must be preprocessed.

See :term:`boson` and :term:`über` and :term:`myon`.

.. comment :term:`ähnlich`.

.. [1] coucou

test-glossary
=============

.. glossary::
   :sorted:

   boson
      Particle with integer spin.

   *fermion*
      Particle with half-integer spin.

   tauon
   myon
   electron
      Examples for fermions.

   über
      Gewisse

   .. änhlich
       Dinge

and obtain this output in pdf:

The current PR has a potential limitation if a term has a footnote. But in fact, adding a footnote to a term in a glossary causes a problem, the term is not indexed properly. Anyway, the alternative approach is currently available at https://github.com/jfbu/sphinx/tree/9985_latex_on_master_v2 (test files not updated). It is cleaner approach perhaps, with less LaTeX macro definitions, and more mark-up output from Sphinx latex writer.

[jfbu]

Probably the fulllineitems environment with \pysigline for object signatures and description should be refactored to use similar parbox dimensions as here. The approach of https://github.com/jfbu/sphinx/tree/9985_latex_on_master_v2 shows how perhaps a refactoring of support for multi-line signatures should be done, in a somewhat cleaner way than current approach in sphinxlatexobjects.sty which has too complicated TeX macros.

But I am delaying that to perhaps another PR which could replace this one with the https://github.com/jfbu/sphinx/tree/9985_latex_on_master_v2 approach and at the same time unify with handling of object descriptions.

[tk0miya]

Thank you for your work, as always :-)
LGTM!

[jfbu]

mypy test fails after merging master branch into this one, but this regards files unrelated to this PR: https://github.com/sphinx-doc/sphinx/runs/4610549456?check_suite_focus=true

[tk0miya]

I fixed the warnings from mypy on the HEAD of master branch now. So please merge it to your branch.

[jfbu]

@tk0miya tests pass after merging master, now merging into master, thanks