Added optional MockObject rules and fixtures to phpstan

[mikadamczyk]

🎫 Issue	N/A

Description:

This PR adds two opt‑in PHPStan rules that enforce correct typing for PHPUnit mocks:

• RequireMockObjectInPropertyTypeRule - catches properties typed only via @var …&MockObject and requires an intersection type on the property itself.
• RequireConcreteTypeForMockReturnRule - Flags methods that return a mock but declare only MockObject as the return type. (Returning a concrete type, even when the value is a mock, is allowed.)

How to enable in a package
The rules are opt‑in via a dedicated include file:

phpstan.neon in your package:

  includes:
    - vendor/ibexa/phpstan/extension.neon
    - vendor/ibexa/phpstan/extension-mocks.neon

Examples

• ✅ private ContentService&MockObject $contentService;
• ✅ private function createContentInfo(): ContentInfo&MockObject
• ✅ private function createContentInfo(): ContentInfo (allowed if you don’t need MockObject typing)
• ❌ /** @var ContentService&MockObject */ private ContentService $contentService;
• ❌ private function createContentInfo(): ContentInfo (when it returns $this->createMock())

Additional notes

• Test fixtures for the rules live under tests/rules/data/ and are excluded from the phpstan package analysis via excludePaths.
• Added .gitignore to keep local caches and vendor/ out of version control.

For QA:

Documentation: