Collection cache key is built differently on read than on write

[guiwoda]

This one's a quick bugfix that would be better if we could refactor key building logic inside the \Doctrine\ORM\Cache implementations, but that would be a (albeit small) BC break in its current API.

I intentionally named the refactored protected method exactly as its named in \Doctrine\ORM\DefaultCache.

Testing this proved harder than what it's worth. I'm actually patching this in userland, and you'll find the bug and correction pretty obvious if you look at both the modified class and \Doctrine\ORM\DefaultCache, so I hope we can merge this one and maybe work on a full test suite for all of the Persister strategies.

Cheers!

[doctrinebot]

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[guilhermeblanco]

I saw that while inspecting another issue. Will merge as soon as unit tests pass.
We do have a SLC test suite, but I think it's not covering all scenarios (being really hard to debug all scenarios over this tbh)