Split up logic in sphinx.transforms.i18n.Locale.apply

[jeanas]

Before, the apply method was one big 400-line chunk. This just splits it up into more manageable chunks by introducing a _NodeUpdater auxiliary class holding logic for updating various types of references.

Feature or Bugfix

• Refactoring

Purpose

Make the Locale transform easier to understand and modify.

[jeanas]

To give a bit of context, I did this as a prelude to trying my hand on actual functionality changes (like for #11157). I was finding the Locale transform pretty hard to follow.

[jeanas]

Would anyone be able to review this PR? I understand that this is not necessarily the most fun type of PR, as it doesn't add anything by itself, but I have some planned i18n improvements that depend on it.

[m-aciek]

For some reason test_intl::test_gettext_dont_rebuild_mo test fails on Windows: https://github.com/sphinx-doc/sphinx/actions/runs/4180689136/jobs/7241911966.

>       assert get_number_of_update_targets(app0) == 0
E       AssertionError: assert 1 == 0
E        +  where 1 = <function test_gettext_dont_rebuild_mo.<locals>.get_number_of_update_targets at 0x000001F791A3B5F0>(<SphinxTestApp buildername='dummy'>)

[AA-Turner]

Thank you @jeanas!

A

[jeanas]

Sorry for leaving those type errors! Thank you for taking care of them yourself, I wasn't expecting it from a busy maintainer.

The failed test seems flaky? I'm not sure why it failed, but it then passed on master.