magento/composer does not support PHP 7.2

[buskamuza]

Update https://github.com/magento/composer, so it supports PHP 7.2

Repo: https://github.com/magento-engcom/magento-composer-php-7.2-support

AC:

• https://github.com/magento-engcom/magento-composer-php-7.2-support/blob/engcom-master/composer.json#L11 includes ~7.2.0
• Setup scenarios pass on PHP 7.2 installation

Scenarios:

• Web Setup Wizard: list, update, install an extension
• Web Setup Wizard: upgrade Magento application to the next version
• Magento CLI setup:install
• Magento CLI setup:upgrade
• Magento CLI module:enable
• Magento CLI module:disable
• Cloud setup/deployment

[buskamuza]

@piotrekkaminski , please review test scenarios and add more scenarios if necessary.

[buskamuza]

@giabmf11 , https://github.com/magento/composer/blob/master/composer.json#L11 doesn't include PHP 7.2 in the list of supported versions. So it should be added and validated that it's really supported. I updated the description.

[piotrekkaminski]

what about removing an extension? is it supported?
what about manual composer commands
cloud setup/deployment needs to be tested as a scenario