Improve ArrayTest structure and readability

[zhukoff74]

This is:

• a bugfix
• a new feature
• refactoring
• additional unit tests

Checklist:

• Changes are covered by unit tests
  • Changes are covered by existing unit tests
  • New unit tests have been added
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change and a link to the pull request if applicable
• Documentation is updated as necessary

Why this change is needed?

• add setUp() and tearDown() methods
• add private method setupMatrix() to set up test data
• improved testMultiDimensionalArrayIsFlattened()
• testPropagateStatic() is divided into separate tests
• testReturnTypes() is divided into separate tests

Tests have become more modular, readable, and easier to maintain. Each test verifies one specific piece of functionality.

[zhukoff74]

Hello, I see an error in php-cs-fixer. What is the best way to fix this, make a new pull request?