Add support for generics via static analysis

[alcaeus]

As was done in doctrine/collections, we should add support for generics using the @psalm-template annotations for generic classes like Repositories and Registries. We should also ensure that generics in PHPStan are supported as well.

See doctrine/collections#177 for the reference implementation in collections.

[alcaeus]

https://github.com/weirdan/doctrine-psalm-plugin was brought to my attention today. @weirdan would you be open to contributing the annotations to our libraries directly? We've added them to doctrine/collections, but I'd love to see these in all other projects as well.

[weirdan]

But of course! What do I need to do to make that happen?

We should also ensure that generics in PHPStan are supported as well.

For the record, PHPStan reads some @psalm- annotations (including @template) and Psalm may soon start to read @phpstan--prefixed ones.

[alcaeus]

A pull request to master is a great start. If you want we can discuss this tomorrow in the symfony-devs or doctrine Slack 👍

[weirdan]

Unfortunately I won't have time for this before Sunday, so definitely not going to happen tomorrow.

[alcaeus]

No worries at all. I'll be off for most of the next two weeks, so please take some time to enjoy the holidays. No need to rush anything here.

[nschoellhorn]

I am also up for help if needed! Nice to see it get to other Doctrine projects as well.

[alcaeus]

@weirdan @nschoellhorn working with you on annotations was great! Would love to do this again for all persistence libraries. Right @Ocramius?