Add linting tool for documentation

[David Smith]

As Natalia wrote on this ​forum post

Currently, style guidelines for docs are well documented, but checking them is still a manual part of the review process. That often results in extra back-and-forth over small formatting details, which can slow things down. Automating this would help ease that overhead, making reviews more efficient for both contributors and maintainers.

The documentation can be linted with ​sphinx-lint with some modifications such that it works with Django's documentation. Main edits are for Django's .txt extension (vs default .rst) and some additional exceptions for the line length check.

[David Smith]

[PR ​https://github.com/django/django/pull/19549]

[Natalia Bidart]

Thank you David! I'm so looking forward to this :-)

[nessita <124304+nessita@…>]

In 7f9bf35:

Refs #36485 -- Grouped docs checks under a unified make check target.

Added a new 'check' rule to the docs Makefile which runs both the black
and spelling checks.

[Natalia <124304+nessita@…>]

In a9c7d4b7:

[5.2.x] Refs #36485 -- Grouped docs checks under a unified make check target.

Added a new 'check' rule to the docs Makefile which runs both the black
and spelling checks.

Backport of 7f9bf357feac06bb34017e1f6c7a7730b1991ede from main.

[nessita <124304+nessita@…>]

In ef2f16b:

Refs #36485 -- Added sphinx-lint support and make lint rule for docs.

This adds a lint.py script to run sphinx-lint on Django's docs files,
a mathing lint target in the docs/Makefile and docs/make.bat, and
updates docs/requirements.txt accordingly.

[nessita <124304+nessita@…>]

In 6f8e23d1:

Refs #36485 -- Removed unnecessary parentheses in :meth: and :func: roles in docs.

[nessita <124304+nessita@…>]

In 724e5ec6:

Refs #36485 -- Fixed dangling hyphen and unbalanced inline markup in docs.

[nessita <124304+nessita@…>]

In 01a460f2:

Refs #36485 -- Removed trailing spaces and tabs in docs.

[nessita <124304+nessita@…>]

In 4286a23d:

Refs #36485 -- Removed double spaces after periods in sentences.

[nessita <124304+nessita@…>]

In f81e6e3:

Refs #36485 -- Rewrapped docs to 79 columns line length.

Lines in the docs files were manually adjusted to conform to the
79 columns limit per line (plus newline), improving readability and
consistency across the content.

[nessita <124304+nessita@…>]

In 43e4d0a:

Fixed #36485 -- Added lint-docs check in Tox and GitHub Actions.

The check docs target now runs spelling, black, and lint, so all
current documentation quality checks can be run with a single command.

Also documented the lint-docs check's availability and usage.

[nessita <124304+nessita@…>]

In 9efce80:

Refs #36485 -- Ignored line-length formatting changes in git blame.

[GitHub <noreply@…>]

In a6271945:

Refs #36485 -- Corrected docs linter to detect too-long lines at file end.