[DOCS] Use ServerRequestInterface $request parameter in AbstractPlugin

The example of the breaking change to AbstractPlugin (removed in v13)
is missing the third parameter `$request`. It is passed to the
TS userfunc execution [1] [2].

This patch makes the migration example more complete for v12 instances.

[1] https://docs.typo3.org/m/typo3/reference-coreapi/12.4/en-us/ApiOverview/RequestLifeCycle/Typo3Request.html#user-function
[2] https://review.typo3.org/c/Packages/TYPO3.CMS/+/66080

Releases: main, 13.4, 12.4
Resolves: #105880
Related: #92984
Change-Id: I27a2fe9d6ee0c8b25d229a4832382ababbc8cc75
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/87628
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Garvin Hicking <gh@faktor-e.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Garvin Hicking <gh@faktor-e.de>
Tested-by: core-ci <typo3@b13.com>

Author: Franz Holzinger

typo3/sysext/core/Documentation/Changelog/12.0/Breaking-98281-MakeAbstractPluginInternal.rst

@@ -49,9 +49,15 @@ Class before migration:
 ..  code-block:: php
     :caption: EXT:gh_randomcontent/Classes/Plugin/RandomContent.php
 
+    use Psr\Http\Message\ServerRequestInterface;
+
     class RandomContent extends AbstractPlugin
     {
-        public function main(string $content, array $conf): string
+        public function main(
+          string $content,
+          array $conf,
+          ServerRequestInterface $request,
+        ): string
         {
             $this->conf = $conf;
 
@@ -75,6 +81,8 @@ Class after migration:
 ..  code-block:: php
     :caption: EXT:gh_randomcontent/Classes/Plugin/RandomContent.php
 
+    use Psr\Http\Message\ServerRequestInterface;
+
     class RandomContent
     {
         /**
@@ -93,7 +101,11 @@ Class after migration:
             $this->cObj = $cObj;
         }
 
-        public function main(string $content, array $conf): string
+        public function main(
+          string $content,
+          array $conf,
+          ServerRequestInterface $request,
+        ): string
         {
             $this->conf = $conf;
 
@@ -134,4 +146,12 @@ It is also possible to migrate to an Extbase plugin using a controller.
 See the :ref:`Extbase documentation, chapter
 "Frontend Plugins" <t3coreapi:extbase_registration_of_frontend_plugins>`.
 
+..  important::
+
+    The `AbstractPlugin` is :ref:`deprecated <deprecation-100639-1681740974>`
+    through a follow-up change and will be removed in TYPO3 v13. Executing
+    a plugin via the TypoScript userFunc (also utilized the `$request` argument for
+    the `main` method) continues to work, as long as the collection of `AbstractPlugin`
+    methods are ported to the custom user class.
+
 .. index:: Frontend, FullyScanned, ext:frontend