feature #47377 [HttpKernel] Use Accept-Language header even if there are no enabled locales (MatTheCat)

This PR was squashed before being merged into the 6.2 branch.

Discussion
----------

[HttpKernel] Use Accept-Language header even if there are no enabled locales

| Q             | A
| ------------- | ---
| Branch?       | 6.2
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | Fix #47355
| License       | MIT
| Doc PR        | N/A

Don’t really know how I should consider this PR 🤔

It would affect people setting `set_locale_from_accept_language` to `true` with no `enabled_locales` when the request has a preferred language:

- before: set the default locale as request locale
- after: set the preferred language as request locale

Commits
-------

b20d074f66 [HttpKernel] Use Accept-Language header even if there are no enabled locales

Author: fabpot

CHANGELOG.md

@@ -18,7 +18,8 @@ CHANGELOG
    `workflow.state_machine`
  * Add `rate_limiter` configuration option to `messenger.transport` to allow rate limited transports using the RateLimiter component
  * Remove `@internal` tag from secret vaults to allow them to be used directly outside the framework bundle and custom vaults to be added
- * Deprecate "framework.form.legacy_error_messages" config node
+ * Deprecate `framework.form.legacy_error_messages` config node
+ * Set locale from request rather than default locale if `framework.enabled_locales` is empty and `framework.set_locale_from_accept_language` is true
 
 6.1
 ---