Current user missing from language negotiator outside of request context

Adding note about PathProcessorLanguage to the issue summary.

Wrote a draft change record and a test. Let's see if anything breaks.

Appears to have a phpstan failure

Line core/tests/Drupal/Tests/Core/PathProcessor/PathProcessorTest.php
------ --------------------------------------------------------------------
140 Class Drupal\language\HttpKernel\PathProcessorLanguage constructor
invoked with 5 parameters, 4 required.
🪪 arguments.count

Not sure a good rule of thumb but do we think these interfaces could be pretty widely uses in translation contrib modules? Only mention if maybe we should wait till 13 to remove.

I don't really have any strong feelings regarding the deprecation but per the Drupal Code Search:

• 6 modules extend LanguageNegotiator ( a12s_locations → , domain_lang → , drupal_helper → , entity_mesh → , queue_mail → , static_suite → ) but none of them override the constructor
• 0 modules extend LanguageRequestSubscriber
• 0 modules extend PathProcessorLanguage

So those last failures were fun, we actually had tests that were relying on language negotiation not running in order to work. And due to the default configuration that's actually not too far fetched. Wrote a change notice to that end in case anyone encounters that same issue.

Let's see if this is now finally green.