Adding a phpcs.xml file

[dawehner]

It would be kind of nice to ship with a phpcs.xml file. Ideally this would be default at least have the rules be available in core by default, and point to just code running in modules/custom, themes/custom

[gergelypap]

+1

We can use core's ruleset as a starting point: https://github.com/drupal/drupal/blob/8.4.x/core/phpcs.xml.dist

[AlexSkrypnyk]

Since this projects provides tooling via drupal/core-dev, supporting of the configs for that tooling does make sense.

If we decide to do so, we would need to:

1. Add PHPCS configuration to support Coder rules with custom locations as targets.
2. Update CI config to include code standards check using PHPCS