ComponentGenerator hardcodes PHP 7.3.0

Problem/Motivation

\Drupal\Composer\Generator\ComponentGenerator::initialPackageMetadata hardcodes PHP 7.3.0, rather than using Drupal's own minimum requirement.

Steps to reproduce

Proposed resolution

Update to \Drupal::MINIMUM_PHP

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet