Add an "xdr" wrapper to launch dr with xdebug

Problem/Motivation

The flake provides an "xdrush" command that wraps drush with xdebug, to make it really easy to start a cli debugging session with drush.

Drupal 12 does not yet have a compatible drush - but it does have the "dr" CLI that was added to core - and is also available in Drupal 11.4+.

Let's add an "xdr" wrapper to support step debugging dr commands.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes