PHP 8 support

[acelaya]

To be done to support PHP 8

• Fix API tests. They fail massively.

Dependency-related:

• Swoole >=4.5.5
• pdo_sqlsrv >=5.9 (there's a preview beta version, but not stable version yet)
• codesniffer 3.5.7
• doctrine dbal 2.12
• Remove dependency on league/plates [Remove dependency on league/plates #912 ]
• Unreleased version of symfony/mercure (the PR is merged but it's not tagged yet)
• endroid/qrcode >=3.10 (blocked by one of their dependencies) (since this seems quite blocked, pinned to one specific commit in dev-master that includes the fixes, until v3.10 is released)

Result of running composer why-not php:8:

• akrabat/ip-address-middleware Updated dependencies to support PHP 7.3, 7.4 and 8.0, and drops support for PHP 7.0 and 7.1 akrabat/ip-address-middleware#27
• dflydev/fig-cookies PHP 8 Support dflydev/dflydev-fig-cookies#39
• doctrine/migrations Allow PHP 8 in 2.x doctrine/migrations#980
• doctrine/orm
• laminas/laminas-inputfilter
  • laminas/laminas-filter
  • laminas/laminas-validator
• laminas/laminas-paginator (there are many dependencies blocking the update. Pagerfanta might be a good replacement https://github.com/BabDev/Pagerfanta)
• laminas/laminas-servicemanager
• lstrojny/functional-php (possible alternative, with support for PHP 8 already https://github.com/Lambdish/phunctional)
• mezzio/mezzio PHP 8.0 compatiblity and dependency upgrades. mezzio/mezzio#60
  • mezzio/mezzio-template Add PHP 8 support mezzio/mezzio-template#5
• mezzio/mezzio-fastroute Bump dependencies to PHP8 mezzio/mezzio-fastroute#7
• mezzio/mezzio-problem-details PHP 8 support mezzio/mezzio-problem-details#11
• nikolaposa/monolog-factory
  • nikolaposa/cascader
• ocramius/proxy-manager Allow PHP 8 Ocramius/ProxyManager#628 (doctrine/migrations now depends on friendsofphp/proxy-manager-lts, which replaces ocramius/proxy-manager and supports PHP 8)
• phly/phly-event-dispatcher (seems a bit dead. Only shlinkio/shlink-event-dispatcher depends on it, so might make sense to look for alternatives. league/event might be a good option https://event.thephpleague.com/3.0/) Feature/dispatcher update shlink-event-dispatcher#28
• php-middleware/request-id Allow install php8 php-middleware/request-id#14
• shlinkio/shlink-importer