Fixed improper ObjectManager usage and respective unit tests

[drpayyne]

Description

• Fixed improper usage of ObjectManager
• Removed unnecessary method: getCssProcessor()
• Fixed appropriate PHPUnit tests

Manual testing scenarios

• ONLY code change

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)

[m2-assistant]

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[magento-engcom-team]

Hi @dmytro-ch, thank you for the review.
ENGCOM-6176 has been created to process this Pull Request

[m2-assistant]

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