[D10] Add the static analyzer tool PHPStan to Backdrop core

This is a fresh feature in Drupal 10, which sounds like something that we should integrate without our GHA: https://www.drupal.org/node/3258232

Description:

The static analyzer tool PHPStan has been added to Drupal Core. We are running the tool with level 0 (the lowest level). The power of static analyzer is that it can find bugs in your code without having to write tests. PHPStan has been added to the script core/scripts/dev/commit-code-check.sh which is part of the testbot.

The PHPStan configuration file is located at: core/phpstan.neon.dist

The PHPStan file with the skipped exceptions is located at: core/phpstan-baseline.neon

CLI Commands

Running PHPStan on drupal core: vendor/bin/phpstan analyze --configuration=core/phpstan.neon.dist Regenerating the baseline: vendor/bin/phpstan analyze --configuration=core/phpstan.neon.dist --generate-baseline ./core/phpstan-baseline.neon