Change composer.json type to phpcodesniffer standard

Problem/Motivation

Composer allows declaring the type of a package. When no type is declared, the default is "library".

There are various composer plugins that can install (register) external standards with PHP_CodeSniffer:

• https://github.com/higidi/composer-phpcodesniffer-standards-plugin (marked as "abandoned" in Packagist).
• https://github.com/DealerDirect/phpcodesniffer-composer-installer
• https://github.com/SimplyAdmire/ComposerPlugins (marked as "abandoned" in Packagist).

For these installers to work, the package type needs to be set to "phpcodesniffer-standard".

There are also a lot of packages that adhere to this type.

Proposed changes

Adding the following line to the composer.json will make it possible for such packages to install this external PHPCS standard using Composer:

    "type" : "phpcodesniffer-standard"

This will in no way change the existing behaviour of this package for users that do not include one of the packages mentioned above in their projects composer.json.