minor #19780 Refactor Request object documentation and redefine method logic (Spomky)

This PR was submitted for the 7.1 branch but it was merged into the 6.4 branch instead.

Discussion
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Refactor Request object documentation and redefine method logic

Fixes #19748

The documentation for the Request object in the controller documentation has been updated to be more specific. The logic of the `getPreferredLanguage` method has been updated and clarified in Symfony 7.1. An additional step has been added which accounts for languages that match the locale, but exhibit a different script or region. The Response Object section has been moved for better flow and readability.

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Commits
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99df757 Refactor Request object documentation and redefine method logic

Author: javiereguiluz

controller.rst

@@ -623,8 +623,8 @@ For example, imagine you're processing a :doc:`form </forms>` submission::
 
 .. _request-object-info:
 
-The Request and Response Object
--------------------------------
+The Request Object
+------------------
 
 As mentioned :ref:`earlier <controller-request-argument>`, Symfony will
 pass the ``Request`` object to any controller argument that is type-hinted with
@@ -660,6 +660,36 @@ the ``Request`` class::
 The ``Request`` class has several public properties and methods that return any
 information you need about the request.
 
+For example, the method ``getPreferredLanguage`` accepts an array of preferred languages and
+returns the best language for the user, based on the ``Accept-Language`` header.
+The locale is returned with language, script and region, if available (e.g. ``en_US``, ``fr_Latn_CH`` or ``pt``).
+
+Before Symfony 7.1, this method had the following logic:
+
+1. If no locale is set as a parameter, it returns the first language in the
+   ``Accept-Language`` header or ``null`` if the header is empty
+2. If no ``Accept-Language`` header is set, it returns the first locale passed
+   as a parameter.
+3. If a locale is set as a parameter and in the ``Accept-Language`` header,
+   it returns the first exact match.
+4. Then, it returns the first language passed in the ``Accept-Language`` header or as argument.
+
+Starting from Symfony 7.1, the method has an additional step:
+
+1. If no locale is set as a parameter, it returns the first language in the
+   ``Accept-Language`` header or ``null`` if the header is empty
+2. If no ``Accept-Language`` header is set, it returns the first locale passed
+   as a parameter.
+3. If a locale is set as a parameter and in the ``Accept-Language`` header,
+   it returns the first exact match.
+4. If a language matches the locale, but has a different script or region, it returns the first language in the
+   ``Accept-Language`` header that matches the locale's language, script or region combination
+   (e.g. ``fr_CA`` will match ``fr_FR``).
+5. Then, it returns the first language passed in the ``Accept-Language`` header or as argument.
+
+The Response Object
+-------------------
+
 Like the ``Request``, the ``Response`` object has a public ``headers`` property.
 This object is of the type :class:`Symfony\\Component\\HttpFoundation\\ResponseHeaderBag`
 and provides methods for getting and setting response headers. The header names are