Convert ImageEffectsTest & ToolkitTest into Kernel tests

Problem/Motivation

Part of the 🌱 [META] Remove all usages of drupal_static() & drupal_static_reset() Active effort for usages of drupal_static() and drupal_static_reset() in \Drupal\Tests\image\Functional\ImageEffectsTest tests.

• Most of the methods from ImageEffectsTest are not doing any HTTP request. The exception is ::testEffectFormValidationErrors() but its scope could be tested with Kernel rather than Functional test.
• No method from ToolkitTest is doing HTTP requests

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Proposed resolution

• Convert ImageEffectsTest into a Kernel test.
• Convert ToolkitTest into a Kernel test.
• Deprecate \Drupal\FunctionalTests\Image\ToolkitTestBase.
• Add a new trait \Drupal\Tests\Traits\Core\ToolkitTestTrait to provide reusable code.

Remaining tasks

None.

User interface changes

None.

API changes

None.

Data model changes

None.

Release notes snippet

N/A