[!!!][TASK] Remove TYPO3 v12 and PHP 8.1 support

[sbuerk]

This change removes TYPO3 v12 and PHP8.1 support starting
by removing related options in Github Actions , the script
dispatcher Build/Scripts/runTests.sh and related version
constraints in composer.json and ext_emconf.php.

Dependencies and tool chain will be streamlined and updated
in follow-up changes to keep the scope small and clean.

Used command(s):

rm -rf Build/phpstan/Core12 \
&& composer config minimum-stability "dev" \
&& composer config prefer-stable true \
&& composer require --no-update \
    "php":"^8.2 || ^8.3 || ^8.4 || ^8.5" \
    "typo3/cms-backend":"^13.4" \
    "typo3/cms-core":"^13.4" \
&& pkw-dev extemconf:normalize -t 13 . \
&& pkw-dev extemconf:constraints:set \
  -t 13 \
  --constraint='8.2.0-8.5.99' \
  --update-only \
  depends php \
  . \
&& pkw-dev extemconf:constraints:set \
  -t 13 \
  --constraint='13.4.0-13.4.99' \
  --update-only \
  depends typo3 \
  . \
&& pkw-dev extemconf:constraints:set \
  -t 13 \
  --constraint='13.4.0-13.4.99' \
  --update-only \
  depends backend \
  .