Updates to toolchain

• Stonehenge 3 support. Replace docker.sh with docker.so
• Replace drupal/core-dev with drupal/core-dev-pinned
• Require Composer runtime v2: composer req composer-runtime-api:^2
• Change DRUPAL_IMAGE=druidfi/drupal:7.3-web to DRUPAL_IMAGE=druidfi/drupal-web:php-7.3 (ARM support)
• Change druidfi/db:mysql5.7-drupal to druidfi/mariadb:10.5-drupal in docker-compose.yml (ARM support)