EZP-31246: Refactored Test setup to stop relying on Database Handler

[alongosz]

Question	Answer
JIRA issue	EZP-31246 blocking EZP-30921
Type	improvement
Target version	ezplatform-kernel:1.0 (internal package test setup)
BC breaks	no
Tests pass	yes
Doc needed	no

TL;DR; Key points:

1. Yaml test data: ab1c973 and c2ecf1a
2. FixtureImporter: fcaa722
3. Usage of FixtureImporter: a9cfb3a and 1dae04a

Summary of changes

This PR drops most of[1] eZc Database Handler usages from our tests (both integration and unit).
You can review it commit by commit - I tried to keep them as separate as possible, though maintaining an order during reviewing is probably recommended, as some changes rely on previous changes.

The most interesting aspect though, is not the refactoring of query building, but concepts I introduced in order to instantiate test setup. It heavily relied on Database Handler, so had to be changed anyway.

The initial data fixtures were stored in eZ/Publish/Core/Repository/Tests/Service/Integration/Legacy/_fixtures/test_data.php.
The file was big, triggered unnecessary static analysis, and overall was difficult to maintain.

I decided to go with Yaml for Kernel 1.0: eZ/Publish/API/Repository/Tests/_fixtures/Legacy/data/test_data.yaml.
It feels more light for IDE in terms of both viewing and updating. It's obviously still too big, but one thing at a time.
Added via ab1c973 and updated via c2ecf1a.

As an intermediate step, I've upgraded SetupFactory to use that new data file and import it using Doctrine QueryBuilder (7908cea).
This led to another key point, which is moving this responsibility to a set of separate classes. Hence, I've introduced via fcaa722 FixtureImporter with in-memory caching layer and Fixture instances for PHP files (for some cases) and Yaml files (the only one now - test_data.yaml). It greatly improved readability of both Setup Factory (a9cfb3a) and unit tests base TestCase (1dae04a).

Less important thing, but useful in the long run: \eZ\Publish\Core\Persistence\Legacy\Tests\TestCase::getDatabaseConnection now fails a test case on connection error instead of re-throwing. Connection error usually does not require analyzing stack trace anyway. This change will make our test cases fetching connection not to report unhandled exception (dbeb8f7).

You might also wonder why I've dropped some tests via 25dccae (eZ\Publish\Core\Persistence\Doctrine\Tests). Those are for Database Handler being dropped, this is why they're gone.

Other commits are strictly related to refactoring.

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[1] There's still \eZ\Publish\Core\Persistence\Legacy\Tests\TestCase::getDatabaseHandler which I cannot drop until #11 (or PRs to be split from that) are completed and merged.

Checklist:

• PR description is updated.
• Tests are passing.
• Added code follows Coding Standards (use $ composer fix-cs).
• PR is ready for a review.