Remove all services from the TestBase container

Problem/Motivation

TestBase::prepareEnvironment currently builds a minimalistic container with the following services populated manually:

• language.default_values (parameter)
• language.default
• language_manager
• string_translation
• info_parser
• request
• current_user

The language-related services are marked with a @todo: Remove this once this class has no calls to t() and format_plural().

In fact the container populated by TestBase remains virtually unused because most of the test-classes either inherit from KernelTestBase or WebTestBase. These base classes replace the container with one which is fully functional.

Proposed resolution

• Remove all services from the TestBase container.
• Rebase tests which currently extend TestBase directly but still require the string_translation service to KernelTestBase. I.e.: [...]\Common\SizeUnitTest, [...]\Plugin\Discovery\DiscoveryTestBase, [...]\Plugin\PluginTestBase

Remaining tasks

Review.

User interface changes

None.

API changes

None.