PHP 8 Compatibility

[mbabker]

Right now this is based on the 3.x branch with running PHPUnit on each package in isolation. Compatibility on the 2.x branch is going to be at a best effort basis for the adapters because the dependency tree is more complex to build against the monopackage, but the core API should be OK.

Status (as of 19 October 2020):

• Adapters:
  • Doctrine:
    • [x] Collections: Passes
    • [x] DBAL: Passes with DBAL 2.12 and 3.x
    • [x] MongoDB ODM: Non-skipped test passes
    • [x] ORM: Passes with DBAL 2.12
    • [x] PHPCR ODM: Passes
  • [x] Elastica: Passes
  • [x] Solarium: Passes
• Integrations:
  • [x] Twig: Passes
• [x] Core: Passes