Add package.xml for install-php-extensions

[soyuka]

install-php-extensions (mlocati/docker-php-extension-installer) won't list extensions that are only available through PIE (mlocati/docker-php-extension-installer#1295), but it builds any repository that ships a package.xml:

install-php-extensions symfony/php-ext-deepclone@v0.8.9

This makes the extension a one-liner in Dockerfiles that already use it, eg dunglas/symfony-docker, which is where most Symfony 8.1 apps would pick it up.

The file only lists the build sources, so new tests don't need to be added to it. A release now bumps <version>, <date> and <notes> next to PHP_DEEPCLONE_VERSION, and a CI job fails when package.xml and php_deepclone.h disagree.

Checked on the symfony-docker base image (dunglas/frankenphp:1-php8.5, ZTS): install-php-extensions builds it and extension_loaded('deepclone') is true, without package.xml it fails with Unable to find the package.xml file. pear package-validate reports no errors.

Related: dunglas/symfony-docker#972 (uses it, draft until a tag with this file exists), php/frankenphp#2699 (static build).

[nicolas-grekas]

Thanks, v0.8.9 is released.