MSI-2876: Change all fixture paths to module namespace path

[vadimjustus]

Description (*)

Since Magento version 2.3 it is possible to use module name to have a runtime resolved path to the module within the @magentoDataFixture annotations. All absolute paths were replaced e.g. @magentoDataFixture ../../../../app/code/Magento/InventoryApi/Test/_files/stocks.php => @magentoDataFixture Magento_InventoryApi::Test/_files/stocks.php

Fixed Issues (if relevant)

1. Hard coded paths to integration test fixture files makes integration testing difficult #2876: Hard coded paths to integration test fixture files makes integration testing difficult

Manual testing scenarios (*)

1. Install MSI development environment as per documentation at https://github.com/magento/inventory/wiki/Metapackage-Installation-Guide
2. Execute integration tests

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds are green)