Use existing tools/config for PHPCS

[vauxia]

This PR amends some of the recently-added pre-commit hook behavior:

• Remove explicit composer requirement to drupal/coder: It is already a dependency of drupal/core-dev, which is required in the dev section.
  • It can get messy to require something that's already a prerequesite
  • It's not great to put drupal/coder on a production environment, which is why drupal/core-dev is in dev.
• Look for a phpcs.xml file and respect the settings therein. This was already set up here: PHPCS configuration #15
  • Ensures that phpcs works consistently when using ddev phpcs, pre-commit hooks, PHPStorm's auto-validation, etc.
  • Example: runs phpcs with both Drupal and DrupalPractice profiles, as configured in the settings file
• Look for a .ddev folder and a working ddev executable, and run ddev exec phpcs when available.
  • Not all developers have PHP binaries, or use similar versions, outside of the ddev containers.
  • Ensures a consistent version of PHP for testing + deployment
• Also fixes PHP Fatal error: Uncaught Error: Class "\PHP_CodeSniffer\Filters\gitstaged" not found in /home/allie/dev/civicactions/pgov-cms/vendor/squizlabs/php_codesniffer/src/Files/FileList.php:90 error

These changes were added conditionally, which means that neither phpcs.xml nor ddev are required. If these are not present, respect the original behavior ( 'Drupal' standard, vendor/bin/phpcs executable )

[vauxia]

@iris-i I'm hoping you can take a look at this if you have time. At present, I'm not able to commit anything without adding a --no-verify because of case sensitivity on my linux machine.