Migrate doc/bootstrap to Python

[tobiasdiez]

Migrate the shell script doc/bootstrap to Python. This improves performance and is preparation for building the docs simply by running "sphinx", see #41156.

The output should be more or less equivalent, expect for minor formatting changes and better escaping of the generated shell commands.

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies

[github-actions]

Documentation preview for this PR (built with commit dc56c2a; changes) is ready! 🎉
This preview will update shortly after each push to this PR.

[mantepse]

I have no idea how I could help in the reviewing process here. Any hints welcome! (I don't understand shell scripts)

The changes in package.py are purely cosmetic, with the exception of adding read_system_packages, right? (I admit that I almost dislike all of them - with the exception of replacing ' with ", which I don't care about. I find breaking the lines in this way makes the code less readable)

[antonio-rojas]

Doesn't build here

FAILED: [code=1] src/doc/htmlspkg 
/usr/bin/python /build/sagemath-doc-git/src/sage/src/build-docs.py --no-prune-empty-dirs --no-pdf-links reference/spkg html -o src/doc --source /build/sagemath-doc-git/src/build/src/doc
[spkg     ] inventory <https://ipywidgets.readthedocs.io/en/stable/> contains multiple definitions for std:label:examples/Widget Layout.ipynb#display
[spkg     ] building [html]: targets for 467 source files that are out of date
[spkg     ] updating environment: 0 added, 31 changed, 0 removed
[spkg     ] /build/sagemath-doc-git/src/build/src/doc/en/reference/spkg/sagemath_objects.rst:64: WARNING: undefined label: 'spkg_force' [ref.ref]
[spkg     ] The HTML pages are in src/doc/html/en/reference/spkg.
Error building the documentation.
Traceback (most recent call last):
  File "/build/sagemath-doc-git/src/sage/src/build-docs.py", line 11, in <module>
    main()
    ~~~~^^
  File "/build/sagemath-doc-git/src/sage/src/sage_docbuild/__main__.py", line 548, in main
    build()
    ~~~~~^^
  File "/build/sagemath-doc-git/src/sage/src/sage_docbuild/builders.py", line 669, in _wrapper
    getattr(DocBuilder, build_type)(self, *args, **kwds)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^
  File "/build/sagemath-doc-git/src/sage/src/sage_docbuild/builders.py", line 142, in f
    runsphinx()
    ~~~~~~~~~^^
  File "/build/sagemath-doc-git/src/sage/src/sage_docbuild/sphinxbuild.py", line 325, in runsphinx
    sys.stderr.raise_errors()
    ~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/build/sagemath-doc-git/src/sage/src/sage_docbuild/sphinxbuild.py", line 256, in raise_errors
    raise OSError(self._error)
OSError: /build/sagemath-doc-git/src/build/src/doc/en/reference/spkg/sagemath_objects.rst:64: WARNING: undefined label: 'spkg_force' [ref.ref]

[tobiasdiez]

I thought that was fixed already with f71e2e6. Strange... I don't have time atm, but will look at it end of next week.

[antonio-rojas]

Looks like the bootstrap.py→bootstrap-docs.py rename somehow confuses github, and it generates an invalid patch that doesn't apply correctly. I built directly from your branch and it works fine.